diff --git a/contrib/examples/pngpixel.c b/contrib/examples/pngpixel.c
index b0e72cb5b..9185d518f 100644
--- a/contrib/examples/pngpixel.c
+++ b/contrib/examples/pngpixel.c
@@ -73,7 +73,7 @@ static void
 print_pixel(png_structp png_ptr, png_infop info_ptr, png_const_bytep row,
    png_uint_32 x)
 {
-   const unsigned int bit_depth = png_get_bit_depth(png_ptr, info_ptr);
+   unsigned int bit_depth = png_get_bit_depth(png_ptr, info_ptr);
 
    switch (png_get_color_type(png_ptr, info_ptr))
    {
@@ -87,7 +87,7 @@ print_pixel(png_structp png_ptr, png_infop info_ptr, png_const_bytep row,
        */
       case PNG_COLOR_TYPE_PALETTE:
          {
-            const int index = component(row, x, 0, bit_depth, 1);
+            int index = component(row, x, 0, bit_depth, 1);
             png_colorp palette = NULL;
             int num_palette = 0;
 
diff --git a/contrib/libtests/makepng.c b/contrib/libtests/makepng.c
index e58a61d02..312062bda 100644
--- a/contrib/libtests/makepng.c
+++ b/contrib/libtests/makepng.c
@@ -661,7 +661,7 @@ generate_row(png_bytep row, size_t rowbytes, unsigned int y, int color_type,
       {
          case 1:
             {
-               const png_uint_32 luma = colors[1];
+               png_uint_32 luma = colors[1];
                png_uint_32 x;
 
                for (x=0; x<=size_max; ++x)
@@ -672,8 +672,8 @@ generate_row(png_bytep row, size_t rowbytes, unsigned int y, int color_type,
 
          case 2:
             {
-               const png_uint_32 luma = colors[1];
-               const png_uint_32 alpha = colors[2];
+               png_uint_32 luma = colors[1];
+               png_uint_32 alpha = colors[2];
                png_uint_32 x;
 
                for (x=0; x<size_max; ++x)
@@ -688,9 +688,9 @@ generate_row(png_bytep row, size_t rowbytes, unsigned int y, int color_type,
 
          case 3:
             {
-               const png_uint_32 red = colors[1];
-               const png_uint_32 green = colors[2];
-               const png_uint_32 blue = colors[3];
+               png_uint_32 red = colors[1];
+               png_uint_32 green = colors[2];
+               png_uint_32 blue = colors[3];
                png_uint_32 x;
 
                for (x=0; x<=size_max; ++x)
@@ -707,10 +707,10 @@ generate_row(png_bytep row, size_t rowbytes, unsigned int y, int color_type,
 
          case 4:
             {
-               const png_uint_32 red = colors[1];
-               const png_uint_32 green = colors[2];
-               const png_uint_32 blue = colors[3];
-               const png_uint_32 alpha = colors[4];
+               png_uint_32 red = colors[1];
+               png_uint_32 green = colors[2];
+               png_uint_32 blue = colors[3];
+               png_uint_32 alpha = colors[4];
                png_uint_32 x;
 
                for (x=0; x<=size_max; ++x)
@@ -812,7 +812,7 @@ write_png(const char **name, FILE *fp, int color_type, int bit_depth,
       png_error(png_ptr, "OOM allocating info structure");
 
    {
-      const unsigned int size =
+      unsigned int size =
          image_size_of_type(color_type, bit_depth, colors, small);
       unsigned int ysize;
       png_fixed_point real_gamma = 45455; /* For sRGB */
@@ -824,7 +824,7 @@ write_png(const char **name, FILE *fp, int color_type, int bit_depth,
        */
       if (small)
       {
-         const unsigned int pixel_depth =
+         unsigned int pixel_depth =
             pixel_depth_of_type(color_type, bit_depth);
 
          if (pixel_depth <= 8U)
@@ -1378,10 +1378,10 @@ static void
 insert_sBIT(png_structp png_ptr, png_infop info_ptr, int nparams,
       png_charpp params)
 {
-   const int ct = png_get_color_type(png_ptr, info_ptr);
-   const int c = (ct & PNG_COLOR_MASK_COLOR ? 3 : 1) +
+   int ct = png_get_color_type(png_ptr, info_ptr);
+   int c = (ct & PNG_COLOR_MASK_COLOR ? 3 : 1) +
       (ct & PNG_COLOR_MASK_ALPHA ? 1 : 0);
-   const unsigned int maxval =
+   unsigned int maxval =
       ct & PNG_COLOR_MASK_PALETTE ? 8U : png_get_bit_depth(png_ptr, info_ptr);
    png_color_8 sBIT;
 
@@ -1856,7 +1856,7 @@ main(int argc, char **argv)
 
    /* Check the colors */
    {
-      const unsigned int lim = (color_type == PNG_COLOR_TYPE_PALETTE ? 255U :
+      unsigned int lim = (color_type == PNG_COLOR_TYPE_PALETTE ? 255U :
          (1U<<bit_depth)-1);
       unsigned int i;
 
diff --git a/contrib/libtests/pngimage.c b/contrib/libtests/pngimage.c
index 998d58c50..f130c043d 100644
--- a/contrib/libtests/pngimage.c
+++ b/contrib/libtests/pngimage.c
@@ -1446,7 +1446,7 @@ test_one_file(struct display *dp, const char *filename)
        * unsigned, because some transforms are negative on a 16-bit system.
        */
       unsigned int active = dp->active_transforms;
-      const int exhaustive = (dp->options & EXHAUSTIVE) != 0;
+      int exhaustive = (dp->options & EXHAUSTIVE) != 0;
       unsigned int current = first_transform(active);
       unsigned int bad_transforms = 0;
       unsigned int bad_combo = ~0U;    /* bitwise AND of failing transforms */
@@ -1572,7 +1572,7 @@ do_test(struct display *dp, const char *file)
 }
 
 int
-main(const int argc, const char * const * const argv)
+main(int argc, char **argv)
 {
    /* For each file on the command line test it with a range of transforms */
    int option_end, ilog = 0;
@@ -1674,7 +1674,7 @@ main(const int argc, const char * const * const argv)
          /* Here on any return, including failures, except user/internal issues
           */
          {
-            const int pass = (d.options & STRICT) ?
+            int pass = (d.options & STRICT) ?
                RESULT_STRICT(d.results) : RESULT_RELAXED(d.results);
 
             if (!pass)
diff --git a/contrib/libtests/pngstest.c b/contrib/libtests/pngstest.c
index 45a52b558..c12c54234 100644
--- a/contrib/libtests/pngstest.c
+++ b/contrib/libtests/pngstest.c
@@ -2346,8 +2346,8 @@ static int
 logpixel(const Transform *transform, png_uint_32 x, png_uint_32 y,
    const Pixel *in, const Pixel *calc, const Pixel *out, const char *reason)
 {
-   const png_uint_32 in_format = transform->in_image->image.format;
-   const png_uint_32 out_format = transform->out_image->image.format;
+   png_uint_32 in_format = transform->in_image->image.format;
+   png_uint_32 out_format = transform->out_image->image.format;
 
    png_uint_32 back_format = out_format & ~PNG_FORMAT_FLAG_ALPHA;
    const char *via_linear = "";
@@ -2602,12 +2602,12 @@ compare_two_images(Image *a, Image *b, int via_linear,
    ptrdiff_t strideb = b->stride;
    png_const_bytep rowa = a->buffer+16;
    png_const_bytep rowb = b->buffer+16;
-   const png_uint_32 width = a->image.width;
-   const png_uint_32 height = a->image.height;
-   const png_uint_32 formata = a->image.format;
-   const png_uint_32 formatb = b->image.format;
-   const unsigned int a_sample = PNG_IMAGE_SAMPLE_SIZE(formata);
-   const unsigned int b_sample = PNG_IMAGE_SAMPLE_SIZE(formatb);
+   png_uint_32 width = a->image.width;
+   png_uint_32 height = a->image.height;
+   png_uint_32 formata = a->image.format;
+   png_uint_32 formatb = b->image.format;
+   unsigned int a_sample = PNG_IMAGE_SAMPLE_SIZE(formata);
+   unsigned int b_sample = PNG_IMAGE_SAMPLE_SIZE(formatb);
    int alpha_added, alpha_removed;
    int bchannels;
    png_uint_32 y;
@@ -2790,8 +2790,7 @@ compare_two_images(Image *a, Image *b, int via_linear,
       (formata & (formatb ^ PNG_FORMAT_FLAG_COLOR) & PNG_FORMAT_FLAG_COLOR)))
    {
       /* Was an alpha channel changed? */
-      const png_uint_32 alpha_changed = (formata ^ formatb) &
-         PNG_FORMAT_FLAG_ALPHA;
+      png_uint_32 alpha_changed = (formata ^ formatb) & PNG_FORMAT_FLAG_ALPHA;
 
       /* Was an alpha channel removed?  (The third test.)  If so the direct
        * comparison is only possible if the input alpha is opaque.
@@ -3627,7 +3626,7 @@ main(int argc, char **argv)
 
          if (arg[0] == '-')
          {
-            const int term = (arg[1] == '0' ? 0 : '\n');
+            int term = (arg[1] == '0' ? 0 : '\n');
             unsigned int ich = 0;
 
             /* Loop reading files, use a static buffer to simplify this and just
diff --git a/contrib/libtests/pngvalid.c b/contrib/libtests/pngvalid.c
index 53170f85b..10767ac93 100644
--- a/contrib/libtests/pngvalid.c
+++ b/contrib/libtests/pngvalid.c
@@ -2590,7 +2590,7 @@ static double digitize(double value, int depth, int do_round)
     * rounding and 'do_round' should be 1, if it is 0 the digitized value will
     * be truncated.
     */
-   const unsigned int digitization_factor = (1U << depth) -1;
+   unsigned int digitization_factor = (1U << depth) - 1;
 
    /* Limiting the range is done as a convenience to the caller - it's easier to
     * do it once here than every time at the call site.
@@ -3688,8 +3688,8 @@ init_standard_palette(png_store *ps, png_structp pp, png_infop pi, int npalette,
 
 #ifdef PNG_WRITE_tRNS_SUPPORTED
 static void
-set_random_tRNS(png_structp pp, png_infop pi, const png_byte colour_type,
-   const int bit_depth)
+set_random_tRNS(png_structp pp, png_infop pi, png_byte colour_type,
+   int bit_depth)
 {
    /* To make this useful the tRNS color needs to match at least one pixel.
     * Random values are fine for gray, including the 16-bit case where we know
@@ -3697,7 +3697,7 @@ set_random_tRNS(png_structp pp, png_infop pi, const png_byte colour_type,
     * method as only 65536 different RGB values are generated.
     */
    png_color_16 tRNS;
-   const png_uint_16 mask = (png_uint_16)((1U << bit_depth)-1);
+   png_uint_16 mask = (png_uint_16)((1U << bit_depth)-1);
 
    R8(tRNS); /* makes unset fields random */
 
@@ -4338,7 +4338,7 @@ make_size_image(png_store* const ps, png_byte const colour_type,
 
       /* Make a name and get an appropriate id for the store: */
       char name[FILE_NAME_SIZE];
-      const png_uint_32 id = FILEID(colour_type, bit_depth, 0/*palette*/,
+      png_uint_32 id = FILEID(colour_type, bit_depth, 0/*palette*/,
          interlace_type, w, h, do_interlace);
 
       standard_name_from_id(name, sizeof name, 0, id);
@@ -4414,7 +4414,7 @@ make_size_image(png_store* const ps, png_byte const colour_type,
          for (pass=0; pass<npasses; ++pass)
          {
             /* The following two are for checking the macros: */
-            const png_uint_32 wPass = PNG_PASS_COLS(w, pass);
+            png_uint_32 wPass = PNG_PASS_COLS(w, pass);
 
             /* If do_interlace is set we don't call png_write_row for every
              * row because some of them are empty.  In fact, for a 1x1 image,
@@ -4646,7 +4646,7 @@ make_error(png_store* const ps, png_byte const colour_type,
    Try
    {
       png_infop pi;
-      const png_structp pp = set_store_for_write(ps, &pi, name);
+      png_structp pp = set_store_for_write(ps, &pi, name);
       png_uint_32 w, h;
       gnu_volatile(pp)
 
@@ -5469,14 +5469,14 @@ progressive_row(png_structp ppIn, png_bytep new_row, png_uint_32 y, int pass)
 
 static void
 sequential_row(standard_display *dp, png_structp pp, png_infop pi,
-    const int iImage, const int iDisplay)
+    int iImage, int iDisplay)
 {
-   const int         npasses = dp->npasses;
-   const int         do_interlace = dp->do_interlace &&
+   int npasses = dp->npasses;
+   int do_interlace = dp->do_interlace &&
       dp->interlace_type == PNG_INTERLACE_ADAM7;
-   const png_uint_32 height = standard_height(pp, dp->id);
-   const png_uint_32 width = standard_width(pp, dp->id);
-   const png_store*  ps = dp->ps;
+   png_uint_32 height = standard_height(pp, dp->id);
+   png_uint_32 width = standard_width(pp, dp->id);
+   const png_store* ps = dp->ps;
    int pass;
 
    for (pass=0; pass<npasses; ++pass)
@@ -5870,7 +5870,7 @@ test_size(png_modifier* const pm, png_byte const colour_type,
     */
    static const png_byte hinc[] = {1, 3, 11, 1, 5};
    static const png_byte winc[] = {1, 9, 5, 7, 1};
-   const int save_bdlo = bdlo;
+   int save_bdlo = bdlo;
 
    for (; bdlo <= bdhi; ++bdlo)
    {
@@ -6078,12 +6078,12 @@ image_pixel_init(image_pixel *this, png_const_bytep row, png_byte colour_type,
     png_byte bit_depth, png_uint_32 x, store_palette palette,
     const image_pixel *format /*from pngvalid transform of input*/)
 {
-   const png_byte sample_depth = (png_byte)(colour_type ==
-      PNG_COLOR_TYPE_PALETTE ? 8 : bit_depth);
-   const unsigned int max = (1U<<sample_depth)-1;
-   const int swap16 = (format != 0 && format->swap16);
-   const int littleendian = (format != 0 && format->littleendian);
-   const int sig_bits = (format != 0 && format->sig_bits);
+   png_byte sample_depth =
+      (png_byte)(colour_type == PNG_COLOR_TYPE_PALETTE ? 8 : bit_depth);
+   unsigned int max = (1U<<sample_depth)-1;
+   int swap16 = (format != 0 && format->swap16);
+   int littleendian = (format != 0 && format->littleendian);
+   int sig_bits = (format != 0 && format->sig_bits);
 
    /* Initially just set everything to the same number and the alpha to opaque.
     * Note that this currently assumes a simple palette where entry x has colour
@@ -6101,7 +6101,7 @@ image_pixel_init(image_pixel *this, png_const_bytep row, png_byte colour_type,
       /* This permits the caller to default to the sample value. */
       if (palette != 0)
       {
-         const unsigned int i = this->palette_index;
+         unsigned int i = this->palette_index;
 
          this->red = palette[i].red;
          this->green = palette[i].green;
@@ -6432,8 +6432,8 @@ static void
 image_transform_mod_end(const image_transform *this, image_pixel *that,
     png_const_structp pp, const transform_display *display)
 {
-   const unsigned int scale = (1U<<that->sample_depth)-1;
-   const int sig_bits = that->sig_bits;
+   unsigned int scale = (1U<<that->sample_depth)-1;
+   int sig_bits = that->sig_bits;
 
    UNUSED(this)
    UNUSED(pp)
@@ -6756,19 +6756,19 @@ transform_image_validate(transform_display *dp, png_const_structp pp,
 {
    /* Constants for the loop below: */
    const png_store* const ps = dp->this.ps;
-   const png_byte in_ct = dp->this.colour_type;
-   const png_byte in_bd = dp->this.bit_depth;
-   const png_uint_32 w = dp->this.w;
-   const png_uint_32 h = dp->this.h;
-   const png_byte out_ct = dp->output_colour_type;
-   const png_byte out_bd = dp->output_bit_depth;
-   const png_byte sample_depth = (png_byte)(out_ct ==
-      PNG_COLOR_TYPE_PALETTE ? 8 : out_bd);
-   const png_byte red_sBIT = dp->this.red_sBIT;
-   const png_byte green_sBIT = dp->this.green_sBIT;
-   const png_byte blue_sBIT = dp->this.blue_sBIT;
-   const png_byte alpha_sBIT = dp->this.alpha_sBIT;
-   const int have_tRNS = dp->this.is_transparent;
+   png_byte in_ct = dp->this.colour_type;
+   png_byte in_bd = dp->this.bit_depth;
+   png_uint_32 w = dp->this.w;
+   png_uint_32 h = dp->this.h;
+   png_byte out_ct = dp->output_colour_type;
+   png_byte out_bd = dp->output_bit_depth;
+   png_byte sample_depth =
+      (png_byte)(out_ct == PNG_COLOR_TYPE_PALETTE ? 8 : out_bd);
+   png_byte red_sBIT = dp->this.red_sBIT;
+   png_byte green_sBIT = dp->this.green_sBIT;
+   png_byte blue_sBIT = dp->this.blue_sBIT;
+   png_byte alpha_sBIT = dp->this.alpha_sBIT;
+   int have_tRNS = dp->this.is_transparent;
    double digitization_error;
 
    store_palette out_palette;
@@ -6929,7 +6929,7 @@ transform_end(png_structp ppIn, png_infop pi)
 
 /* A single test run. */
 static void
-transform_test(png_modifier *pmIn, const png_uint_32 idIn,
+transform_test(png_modifier *pmIn, png_uint_32 idIn,
     const image_transform* transform_listIn, const char * const name)
 {
    transform_display d;
@@ -7764,7 +7764,7 @@ static void
 image_transform_png_set_rgb_to_gray_set(const image_transform *this,
     transform_display *that, png_structp pp, png_infop pi)
 {
-   const int error_action = 1; /* no error, no defines in png.h */
+   int error_action = 1; /* no error, no defines in png.h */
 
 #  ifdef PNG_FLOATING_POINT_SUPPORTED
       png_set_rgb_to_gray(pp, error_action, data.red_to_set, data.green_to_set);
@@ -7905,10 +7905,10 @@ image_transform_png_set_rgb_to_gray_mod(const image_transform *this,
 #  if DIGITIZE
       {
          png_modifier *pm = display->pm;
-         const unsigned int sample_depth = that->sample_depth;
-         const unsigned int calc_depth = (pm->assume_16_bit_calculations ? 16 :
+         unsigned int sample_depth = that->sample_depth;
+         unsigned int calc_depth = (pm->assume_16_bit_calculations ? 16 :
             sample_depth);
-         const unsigned int gamma_depth =
+         unsigned int gamma_depth =
             (sample_depth == 16 ?
                display->max_gamma_8 :
                (pm->assume_16_bit_calculations ?
@@ -8002,7 +8002,7 @@ image_transform_png_set_rgb_to_gray_mod(const image_transform *this,
             b * data.blue_coefficient;
 
          {
-            const int do_round = data.gamma != 1 || calc_depth == 16;
+            int do_round = data.gamma != 1 || calc_depth == 16;
             const double ce = 2. / 32768;
 
             graylo = DD(rlo * (data.red_coefficient-ce) +
@@ -8626,7 +8626,7 @@ image_transform_png_set_filler_mod(const image_transform *this,
        (that->colour_type == PNG_COLOR_TYPE_RGB ||
         that->colour_type == PNG_COLOR_TYPE_GRAY))
    {
-      const unsigned int max = (1U << that->bit_depth)-1;
+      unsigned int max = (1U << that->bit_depth)-1;
       that->alpha = data.filler & max;
       that->alphaf = ((double)that->alpha) / max;
       that->alphae = 0;
@@ -8693,7 +8693,7 @@ image_transform_png_set_add_alpha_mod(const image_transform *this,
        (that->colour_type == PNG_COLOR_TYPE_RGB ||
         that->colour_type == PNG_COLOR_TYPE_GRAY))
    {
-      const unsigned int max = (1U << that->bit_depth)-1;
+      unsigned int max = (1U << that->bit_depth)-1;
       that->alpha = data.filler & max;
       that->alphaf = ((double)that->alpha) / max;
       that->alphae = 0;
@@ -8884,7 +8884,7 @@ image_transform_png_set_shift_set(const image_transform *this,
     * field is randomized independently.  This acts as a check that
     * libpng does use the correct field.
     */
-   const unsigned int depth = that->this.bit_depth;
+   unsigned int depth = that->this.bit_depth;
 
    data.red = (png_byte)/*SAFE*/(random_mod(depth)+1);
    data.green = (png_byte)/*SAFE*/(random_mod(depth)+1);
@@ -9304,7 +9304,7 @@ gamma_info_imp(gamma_display *dp, png_structp pp, png_infop pi)
           */
          const double sg = dp->screen_gamma;
 #        ifndef PNG_FLOATING_POINT_SUPPORTED
-            const png_fixed_point g = fix(sg);
+            png_fixed_point g = fix(sg);
 #        endif
 
 #        ifdef PNG_FLOATING_POINT_SUPPORTED
@@ -9352,7 +9352,7 @@ gamma_info_imp(gamma_display *dp, png_structp pp, png_infop pi)
           */
          const double bg = dp->background_gamma;
 #        ifndef PNG_FLOATING_POINT_SUPPORTED
-            const png_fixed_point g = fix(bg);
+            png_fixed_point g = fix(bg);
 #        endif
 
 #        ifdef PNG_FLOATING_POINT_SUPPORTED
@@ -9426,7 +9426,7 @@ static void
 init_validate_info(validate_info *vi, gamma_display *dp, png_const_structp pp,
     int in_depth, int out_depth)
 {
-   const unsigned int outmax = (1U<<out_depth)-1;
+   unsigned int outmax = (1U<<out_depth)-1;
 
    vi->pp = pp;
    vi->dp = dp;
@@ -9588,14 +9588,14 @@ gamma_component_compose(int do_background, double input_sample, double alpha,
 /* This API returns the encoded *input* component, in the range 0..1 */
 static double
 gamma_component_validate(const char *name, const validate_info *vi,
-    const unsigned int id, const unsigned int od,
+    unsigned int id, unsigned int od,
     const double alpha /* <0 for the alpha channel itself */,
     const double background /* component background value */)
 {
-   const unsigned int isbit = id >> vi->isbit_shift;
-   const unsigned int sbit_max = vi->sbit_max;
-   const unsigned int outmax = vi->outmax;
-   const int do_background = vi->do_background;
+   unsigned int isbit = id >> vi->isbit_shift;
+   unsigned int sbit_max = vi->sbit_max;
+   unsigned int outmax = vi->outmax;
+   int do_background = vi->do_background;
 
    double i;
 
@@ -10161,13 +10161,13 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,
 {
    /* Get some constants derived from the input and output file formats: */
    const png_store* const ps = dp->this.ps;
-   const png_byte in_ct = dp->this.colour_type;
-   const png_byte in_bd = dp->this.bit_depth;
-   const png_uint_32 w = dp->this.w;
-   const png_uint_32 h = dp->this.h;
+   png_byte in_ct = dp->this.colour_type;
+   png_byte in_bd = dp->this.bit_depth;
+   png_uint_32 w = dp->this.w;
+   png_uint_32 h = dp->this.h;
    const size_t cbRow = dp->this.cbRow;
-   const png_byte out_ct = png_get_color_type(pp, pi);
-   const png_byte out_bd = png_get_bit_depth(pp, pi);
+   png_byte out_ct = png_get_color_type(pp, pi);
+   png_byte out_bd = png_get_bit_depth(pp, pi);
 
    /* There are three sources of error, firstly the quantization in the
     * file encoding, determined by sbit and/or the file depth, secondly
@@ -10208,11 +10208,11 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,
     * The basic tests below do not do this, however if 'use_input_precision'
     * is set a subsequent test is performed above.
     */
-   const unsigned int samples_per_pixel = (out_ct & 2U) ? 3U : 1U;
+   unsigned int samples_per_pixel = (out_ct & 2U) ? 3U : 1U;
    int processing;
    png_uint_32 y;
    const store_palette_entry *in_palette = dp->this.palette;
-   const int in_is_transparent = dp->this.is_transparent;
+   int in_is_transparent = dp->this.is_transparent;
    int process_tRNS;
    int out_npalette = -1;
    int out_is_transparent = 0; /* Just refers to the palette case */
@@ -10260,9 +10260,9 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,
             double alpha = 1; /* serves as a flag value */
 
             /* Record the palette index for index images. */
-            const unsigned int in_index =
+            unsigned int in_index =
                in_ct == 3 ? sample(std, 3, in_bd, x, 0, 0, 0) : 256;
-            const unsigned int out_index =
+            unsigned int out_index =
                out_ct == 3 ? sample(std, 3, out_bd, x, 0, 0, 0) : 256;
 
             /* Handle input alpha - png_set_background will cause the output
@@ -10271,7 +10271,7 @@ gamma_image_validate(gamma_display *dp, png_const_structp pp,
             if ((in_ct & PNG_COLOR_MASK_ALPHA) != 0 ||
                 (in_ct == 3 && in_is_transparent))
             {
-               const unsigned int input_alpha = in_ct == 3 ?
+               unsigned int input_alpha = in_ct == 3 ?
                   dp->this.palette[in_index].alpha :
                   sample(std, in_ct, in_bd, x, samples_per_pixel, 0, 0);
 
@@ -10396,14 +10396,14 @@ gamma_end(png_structp ppIn, png_infop pi)
  * maxpc:  maximum percentage error (as a percentage)
  */
 static void
-gamma_test(png_modifier *pmIn, const png_byte colour_typeIn,
-    const png_byte bit_depthIn, const int palette_numberIn,
-    const int interlace_typeIn,
+gamma_test(png_modifier *pmIn, png_byte colour_typeIn,
+    png_byte bit_depthIn, int palette_numberIn,
+    int interlace_typeIn,
     const double file_gammaIn, const double screen_gammaIn,
-    const png_byte sbitIn, const int threshold_testIn,
+    png_byte sbitIn, int threshold_testIn,
     const char *name,
-    const int use_input_precisionIn, const int scale16In,
-    const int expand16In, const int do_backgroundIn,
+    int use_input_precisionIn, int scale16In,
+    int expand16In, int do_backgroundIn,
     const png_color_16 *bkgd_colorIn, double bkgd_gammaIn)
 {
    gamma_display d;
@@ -10607,11 +10607,11 @@ perform_gamma_threshold_tests(png_modifier *pm)
 }
 
 static void gamma_transform_test(png_modifier *pm,
-   const png_byte colour_type, const png_byte bit_depth,
-   const int palette_number,
-   const int interlace_type, const double file_gamma,
-   const double screen_gamma, const png_byte sbit,
-   const int use_input_precision, const int scale16)
+   png_byte colour_type, png_byte bit_depth,
+   int palette_number,
+   int interlace_type, const double file_gamma,
+   const double screen_gamma, png_byte sbit,
+   int use_input_precision, int scale16)
 {
    size_t pos = 0;
    char name[64];
@@ -10768,12 +10768,12 @@ static void perform_gamma_scale16_tests(png_modifier *pm)
 #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
    defined(PNG_READ_ALPHA_MODE_SUPPORTED)
 static void gamma_composition_test(png_modifier *pm,
-   const png_byte colour_type, const png_byte bit_depth,
-   const int palette_number,
-   const int interlace_type, const double file_gamma,
+   png_byte colour_type, png_byte bit_depth,
+   int palette_number,
+   int interlace_type, const double file_gamma,
    const double screen_gamma,
-   const int use_input_precision, const int do_background,
-   const int expand_16)
+   int use_input_precision, int do_background,
+   int expand_16)
 {
    size_t pos = 0;
    png_const_charp base;
diff --git a/contrib/libtests/tarith.c b/contrib/libtests/tarith.c
index c95226f03..c03f05a80 100644
--- a/contrib/libtests/tarith.c
+++ b/contrib/libtests/tarith.c
@@ -331,8 +331,8 @@ static int check_one_character(checkfp_command *co, checkfp_control c, int ch)
     */
    size_t index = 0;
    const char test = (char)ch;
-   const int number_is_valid = png_check_fp_number(&test, 1, &c.state, &index);
-   const int character_accepted = (index == 1);
+   int number_is_valid = png_check_fp_number(&test, 1, &c.state, &index);
+   int character_accepted = (index == 1);
 
    if (c.check_state != exponent && isdigit(ch) && ch != '0')
       c.is_zero = 0;
diff --git a/contrib/powerpc-vsx/linux_aux.c b/contrib/powerpc-vsx/linux_aux.c
index 796922d77..7828acafb 100644
--- a/contrib/powerpc-vsx/linux_aux.c
+++ b/contrib/powerpc-vsx/linux_aux.c
@@ -23,14 +23,12 @@
 static int
 png_have_vsx(png_structp png_ptr)
 {
-
-   const unsigned long auxv = getauxval( AT_HWCAP );
+   unsigned long auxv = getauxval(AT_HWCAP);
 
    PNG_UNUSED(png_ptr)
 
-   if(auxv & (PPC_FEATURE_HAS_ALTIVEC|PPC_FEATURE_HAS_VSX ))
+   if(auxv & (PPC_FEATURE_HAS_ALTIVEC|PPC_FEATURE_HAS_VSX))
       return 1;
    else
       return 0;
 }
-
diff --git a/contrib/tools/pngcp.c b/contrib/tools/pngcp.c
index f6a0d50f4..1a39129a0 100644
--- a/contrib/tools/pngcp.c
+++ b/contrib/tools/pngcp.c
@@ -735,7 +735,7 @@ option_index(struct display *dp, const char *opt, size_t len)
 static int
 get_option(struct display *dp, const char *opt, int *value)
 {
-   const png_byte i = option_index(dp, opt, strlen(opt));
+   png_byte i = option_index(dp, opt, strlen(opt));
 
    if (dp->entry[i]) /* option was set on command line */
    {
@@ -789,7 +789,7 @@ record_opt(struct display *dp, png_byte opt, const char *entry_name)
     * numerical value.
     */
 {
-   const unsigned int sp = dp->csp; /* stack entry of next searched option */
+   unsigned int sp = dp->csp; /* stack entry of next searched option */
 
    if (sp >= dp->tsp)
    {
@@ -797,7 +797,7 @@ record_opt(struct display *dp, png_byte opt, const char *entry_name)
        * searched entry or the start of the dp->curr buffer if there is nothing
        * on the stack yet (sp == 0).
        */
-      const int offset = set_opt_string_(dp, sp, opt, entry_name);
+      int offset = set_opt_string_(dp, sp, opt, entry_name);
 
       if (sp > 0)
          dp->stack[sp-1].opt_string_end = offset;
@@ -1222,7 +1222,7 @@ advance_opt(struct display *dp, png_byte opt, int search)
 }
 
 static int
-getallopts_(struct display *dp, const png_byte opt, int *value, int record)
+getallopts_(struct display *dp, png_byte opt, int *value, int record)
    /* Like getop but iterate over all the values if the option was set to "all".
     */
 {
@@ -1259,7 +1259,7 @@ getsearchopts(struct display *dp, const char *opt_str, int *value)
    /* As above except that if the option was not set try a search */
 {
    png_byte istrat;
-   const png_byte opt = option_index(dp, opt_str, strlen(opt_str));
+   png_byte opt = option_index(dp, opt_str, strlen(opt_str));
    int record = options[opt].search;
    const char *entry_name;
 
@@ -2302,7 +2302,7 @@ cppng(struct display *dp, const char *file, const char *gv dest)
 }
 
 int
-main(const int argc, const char * const * const argv)
+main(int argc, char **argv)
 {
    /* For each file on the command line test it with a range of transforms */
    int option_end;
@@ -2379,7 +2379,7 @@ main(const int argc, const char * const * const argv)
          /* Here on any return, including failures, except user/internal issues
           */
          {
-            const int pass = (d.options & STRICT) ?
+            int pass = (d.options & STRICT) ?
                RESULT_STRICT(d.results) : RESULT_RELAXED(d.results);
 
             if (!pass)
diff --git a/contrib/tools/pngfix.c b/contrib/tools/pngfix.c
index f494230d8..483a593f2 100644
--- a/contrib/tools/pngfix.c
+++ b/contrib/tools/pngfix.c
@@ -2514,7 +2514,7 @@ zlib_run(struct zlib *zlib)
        */
       for (;;)
       {
-         const unsigned int count = list->count;
+         unsigned int count = list->count;
          unsigned int i;
 
          for (i = 0; i<count; ++i)
@@ -2791,7 +2791,7 @@ process_chunk(struct file *file, png_uint_32 file_crc, png_uint_32 next_length,
     * to read_chunk.
     */
 {
-   const png_uint_32 type = file->type;
+   png_uint_32 type = file->type;
 
    if (file->global->verbose > 1)
    {
diff --git a/libpng.3 b/libpng.3
index 0f9b8f27e..4230d54e7 100644
--- a/libpng.3
+++ b/libpng.3
@@ -353,7 +353,7 @@ libpng \- Portable Network Graphics (PNG) Reference Library 1.6.36.git
 
 \fBvoid png_set_eXIf (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fIexif\fP\fB);\fP
 
-\fBvoid png_set_eXIf_1 (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, const png_uint_32 \fP\fInum_exif\fP\fB, png_bytep \fIexif\fP\fB);\fP
+\fBvoid png_set_eXIf_1 (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fInum_exif\fP\fB, png_bytep \fIexif\fP\fB);\fP
 
 \fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
 
diff --git a/png.c b/png.c
index 74293c859..d5590ae51 100644
--- a/png.c
+++ b/png.c
@@ -3970,18 +3970,18 @@ png_gamma_correct(png_structrp png_ptr, unsigned int value,
  */
 static void
 png_build_16bit_table(png_structrp png_ptr, png_uint_16pp *ptable,
-    const unsigned int shift, const png_fixed_point gamma_val)
+    unsigned int shift, png_fixed_point gamma_val)
 {
    /* Various values derived from 'shift': */
-   const unsigned int num = 1U << (8U - shift);
+   unsigned int num = 1U << (8U - shift);
 #ifdef PNG_FLOATING_ARITHMETIC_SUPPORTED
    /* CSE the division and work round wacky GCC warnings (see the comments
     * in png_gamma_8bit_correct for where these come from.)
     */
    const double fmax = 1./(((png_int_32)1 << (16U - shift))-1);
 #endif
-   const unsigned int max = (1U << (16U - shift))-1U;
-   const unsigned int max_by_2 = 1U << (15U-shift);
+   unsigned int max = (1U << (16U - shift))-1U;
+   unsigned int max_by_2 = 1U << (15U-shift);
    unsigned int i;
 
    png_uint_16pp table = *ptable =
@@ -4047,10 +4047,10 @@ png_build_16bit_table(png_structrp png_ptr, png_uint_16pp *ptable,
  */
 static void
 png_build_16to8_table(png_structrp png_ptr, png_uint_16pp *ptable,
-    const unsigned int shift, const png_fixed_point gamma_val)
+    unsigned int shift, png_fixed_point gamma_val)
 {
-   const unsigned int num = 1U << (8U - shift);
-   const unsigned int max = (1U << (16U - shift))-1U;
+   unsigned int num = 1U << (8U - shift);
+   unsigned int max = (1U << (16U - shift))-1U;
    unsigned int i;
    png_uint_32 last;
 
@@ -4115,7 +4115,7 @@ png_build_16to8_table(png_structrp png_ptr, png_uint_16pp *ptable,
  */
 static void
 png_build_8bit_table(png_structrp png_ptr, png_bytepp ptable,
-    const png_fixed_point gamma_val)
+    png_fixed_point gamma_val)
 {
    unsigned int i;
    png_bytep table = *ptable = (png_bytep)png_malloc(png_ptr, 256);
diff --git a/png.h b/png.h
index ab3424aee..96177ccf3 100644
--- a/png.h
+++ b/png.h
@@ -1963,12 +1963,12 @@ PNG_FIXED_EXPORT(233, void, png_set_cHRM_XYZ_fixed, (png_const_structrp png_ptr,
 PNG_EXPORT(246, png_uint_32, png_get_eXIf, (png_const_structrp png_ptr,
     png_inforp info_ptr, png_bytep *exif));
 PNG_EXPORT(247, void, png_set_eXIf, (png_const_structrp png_ptr,
-    png_inforp info_ptr, const png_bytep exif));
+    png_inforp info_ptr, png_bytep exif));
 
 PNG_EXPORT(248, png_uint_32, png_get_eXIf_1, (png_const_structrp png_ptr,
     png_const_inforp info_ptr, png_uint_32 *num_exif, png_bytep *exif));
 PNG_EXPORT(249, void, png_set_eXIf_1, (png_const_structrp png_ptr,
-    png_inforp info_ptr, const png_uint_32 num_exif, const png_bytep exif));
+    png_inforp info_ptr, png_uint_32 num_exif, png_bytep exif));
 #endif
 
 #ifdef PNG_gAMA_SUPPORTED
diff --git a/pngerror.c b/pngerror.c
index 89a49039c..ec3a709b9 100644
--- a/pngerror.c
+++ b/pngerror.c
@@ -885,7 +885,7 @@ PNG_FUNCTION(void /* PRIVATE */, (PNGCBAPI
 png_safe_error),(png_structp png_nonconst_ptr, png_const_charp error_message),
     PNG_NORETURN)
 {
-   const png_const_structrp png_ptr = png_nonconst_ptr;
+   png_const_structrp png_ptr = png_nonconst_ptr;
    png_imagep image = png_voidcast(png_imagep, png_ptr->error_ptr);
 
    /* An error is always logged here, overwriting anything (typically a warning)
@@ -920,7 +920,7 @@ png_safe_error),(png_structp png_nonconst_ptr, png_const_charp error_message),
 void /* PRIVATE */ PNGCBAPI
 png_safe_warning(png_structp png_nonconst_ptr, png_const_charp warning_message)
 {
-   const png_const_structrp png_ptr = png_nonconst_ptr;
+   png_const_structrp png_ptr = png_nonconst_ptr;
    png_imagep image = png_voidcast(png_imagep, png_ptr->error_ptr);
 
    /* A warning is only logged if there is no prior warning or error. */
diff --git a/pngpriv.h b/pngpriv.h
index acaf15ccc..a23febb81 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -1537,10 +1537,10 @@ PNG_INTERNAL_FUNCTION(void,png_handle_zTXt,(png_structrp png_ptr,
 #endif
 
 PNG_INTERNAL_FUNCTION(void,png_check_chunk_name,(png_const_structrp png_ptr,
-    const png_uint_32 chunk_name),PNG_EMPTY);
+    png_uint_32 chunk_name),PNG_EMPTY);
 
 PNG_INTERNAL_FUNCTION(void,png_check_chunk_length,(png_const_structrp png_ptr,
-    const png_uint_32 chunk_length),PNG_EMPTY);
+    png_uint_32 chunk_length),PNG_EMPTY);
 
 PNG_INTERNAL_FUNCTION(void,png_handle_unknown,(png_structrp png_ptr,
     png_inforp info_ptr, png_uint_32 length, int keep),PNG_EMPTY);
diff --git a/pngread.c b/pngread.c
index 9c477c1bf..f8e762196 100644
--- a/pngread.c
+++ b/pngread.c
@@ -1758,9 +1758,9 @@ png_create_colormap_entry(png_image_read_control *display,
     png_uint_32 alpha, int encoding)
 {
    png_imagep image = display->image;
-   const int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
+   int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
        P_LINEAR : P_sRGB;
-   const int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
+   int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
        (red != green || green != blue);
 
    if (ip > 255)
@@ -1869,13 +1869,13 @@ png_create_colormap_entry(png_image_read_control *display,
    /* Store the value. */
    {
 #     ifdef PNG_FORMAT_AFIRST_SUPPORTED
-         const int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
+         int afirst = (image->format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
             (image->format & PNG_FORMAT_FLAG_ALPHA) != 0;
 #     else
 #        define afirst 0
 #     endif
 #     ifdef PNG_FORMAT_BGR_SUPPORTED
-         const int bgr = (image->format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
+         int bgr = (image->format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
 #     else
 #        define bgr 0
 #     endif
@@ -2085,11 +2085,11 @@ png_image_read_colormap(png_voidp argument)
 {
    png_image_read_control *display =
       png_voidcast(png_image_read_control*, argument);
-   const png_imagep image = display->image;
+   png_imagep image = display->image;
 
-   const png_structrp png_ptr = image->opaque->png_ptr;
-   const png_uint_32 output_format = image->format;
-   const int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
+   png_structrp png_ptr = image->opaque->png_ptr;
+   png_uint_32 output_format = image->format;
+   int output_encoding = (output_format & PNG_FORMAT_FLAG_LINEAR) != 0 ?
       P_LINEAR : P_sRGB;
 
    unsigned int cmap_entries;
@@ -2802,7 +2802,7 @@ png_image_read_colormap(png_voidp argument)
             unsigned int num_trans = png_ptr->num_trans;
             png_const_bytep trans = num_trans > 0 ? png_ptr->trans_alpha : NULL;
             png_const_colorp colormap = png_ptr->palette;
-            const int do_background = trans != NULL &&
+            int do_background = trans != NULL &&
                (output_format & PNG_FORMAT_FLAG_ALPHA) == 0;
             unsigned int i;
 
@@ -3946,7 +3946,7 @@ png_image_read_direct(png_voidp argument)
        */
       if (linear != 0)
       {
-         const png_uint_16 le = 0x0001;
+         png_uint_16 le = 0x0001;
 
          if ((*(png_const_bytep) & le) != 0)
             png_set_swap(png_ptr);
@@ -4108,7 +4108,7 @@ png_image_finish_read(png_imagep image, png_const_colorp background,
        * original PNG format because it may not occur in the output PNG format
        * and libpng deals with the issues of reading the original.
        */
-      const unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
+      unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
 
       /* The following checks just the 'row_stride' calculation to ensure it
        * fits in a signed 32-bit value.  Because channels/components can be
@@ -4119,7 +4119,7 @@ png_image_finish_read(png_imagep image, png_const_colorp background,
       if (image->width <= 0x7fffffffU/channels) /* no overflow */
       {
          png_uint_32 check;
-         const png_uint_32 png_row_stride = image->width * channels;
+         png_uint_32 png_row_stride = image->width * channels;
 
          if (row_stride == 0)
             row_stride = (png_int_32)/*SAFE*/png_row_stride;
diff --git a/pngrtran.c b/pngrtran.c
index e61be8782..6b9b7202f 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -2986,7 +2986,6 @@ png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
  */
 static int
 png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
-
 {
    int rgb_error = 0;
 
@@ -2995,12 +2994,11 @@ png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
    if ((row_info->color_type & PNG_COLOR_MASK_PALETTE) == 0 &&
        (row_info->color_type & PNG_COLOR_MASK_COLOR) != 0)
    {
-      const png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
-      const png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
-      const png_uint_32 bc = 32768 - rc - gc;
-      const png_uint_32 row_width = row_info->width;
-      const int have_alpha =
-         (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;
+      png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
+      png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
+      png_uint_32 bc = 32768 - rc - gc;
+      png_uint_32 row_width = row_info->width;
+      int have_alpha = (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;
 
       if (row_info->bit_depth == 8)
       {
@@ -4143,12 +4141,11 @@ png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
    {
       if (row_info->bit_depth == 8)
       {
-         const png_bytep table = png_ptr->gamma_from_1;
+         png_bytep table = png_ptr->gamma_from_1;
 
          if (table != NULL)
          {
-            const int step =
-               (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;
+            int step = (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;
 
             /* The alpha channel is the last component: */
             row += step - 1;
@@ -4162,13 +4159,12 @@ png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
 
       else if (row_info->bit_depth == 16)
       {
-         const png_uint_16pp table = png_ptr->gamma_16_from_1;
-         const int gamma_shift = png_ptr->gamma_shift;
+         png_uint_16pp table = png_ptr->gamma_16_from_1;
+         int gamma_shift = png_ptr->gamma_shift;
 
          if (table != NULL)
          {
-            const int step =
-               (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;
+            int step = (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;
 
             /* The alpha channel is the last component: */
             row += step - 2;
diff --git a/pngrutil.c b/pngrutil.c
index 1c4c9750f..d5fa08c39 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -1461,8 +1461,7 @@ png_handle_iCCP(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
                {
                   /* We have the ICC profile header; do the basic header checks.
                    */
-                  const png_uint_32 profile_length =
-                     png_get_uint_32(profile_header);
+                  png_uint_32 profile_length = png_get_uint_32(profile_header);
 
                   if (png_icc_check_length(png_ptr, &png_ptr->colorspace,
                       keyword, profile_length) != 0)
@@ -1479,8 +1478,8 @@ png_handle_iCCP(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
                          * profile.  The header check has already validated
                          * that none of this stuff will overflow.
                          */
-                        const png_uint_32 tag_count = png_get_uint_32(
-                            profile_header+128);
+                        png_uint_32 tag_count =
+                           png_get_uint_32(profile_header + 128);
                         png_bytep profile = png_read_buffer(png_ptr,
                             profile_length, 2/*silent*/);
 
@@ -3132,7 +3131,7 @@ png_handle_unknown(png_structrp png_ptr, png_inforp info_ptr,
  */
 
 void /* PRIVATE */
-png_check_chunk_name(png_const_structrp png_ptr, const png_uint_32 chunk_name)
+png_check_chunk_name(png_const_structrp png_ptr, png_uint_32 chunk_name)
 {
    int i;
    png_uint_32 cn=chunk_name;
@@ -3151,7 +3150,7 @@ png_check_chunk_name(png_const_structrp png_ptr, const png_uint_32 chunk_name)
 }
 
 void /* PRIVATE */
-png_check_chunk_length(png_const_structrp png_ptr, const png_uint_32 length)
+png_check_chunk_length(png_const_structrp png_ptr, png_uint_32 length)
 {
    png_alloc_size_t limit = PNG_UINT_31_MAX;
 
diff --git a/pngset.c b/pngset.c
index d1d735480..ec75dbe36 100644
--- a/pngset.c
+++ b/pngset.c
@@ -137,7 +137,7 @@ png_set_cHRM_XYZ(png_const_structrp png_ptr, png_inforp info_ptr, double red_X,
 #ifdef PNG_eXIf_SUPPORTED
 void PNGAPI
 png_set_eXIf(png_const_structrp png_ptr, png_inforp info_ptr,
-    const png_bytep eXIf_buf)
+    png_bytep eXIf_buf)
 {
   png_warning(png_ptr, "png_set_eXIf does not work; use png_set_eXIf_1");
   PNG_UNUSED(info_ptr)
@@ -146,7 +146,7 @@ png_set_eXIf(png_const_structrp png_ptr, png_inforp info_ptr,
 
 void PNGAPI
 png_set_eXIf_1(png_const_structrp png_ptr, png_inforp info_ptr,
-    const png_uint_32 num_exif, const png_bytep eXIf_buf)
+    png_uint_32 num_exif, png_bytep eXIf_buf)
 {
    int i;
 
diff --git a/pngwrite.c b/pngwrite.c
index 052a47c57..98bce0e35 100644
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -1536,7 +1536,7 @@ png_write_image_16bit(png_voidp argument)
        display->first_row);
    png_uint_16p output_row = png_voidcast(png_uint_16p, display->local_row);
    png_uint_16p row_end;
-   const unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
+   unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
        3 : 1;
    int aindex = 0;
    png_uint_32 y = image->height;
@@ -1573,7 +1573,7 @@ png_write_image_16bit(png_voidp argument)
 
       while (out_ptr < row_end)
       {
-         const png_uint_16 alpha = in_ptr[aindex];
+         png_uint_16 alpha = in_ptr[aindex];
          png_uint_32 reciprocal = 0;
          int c;
 
@@ -1695,7 +1695,7 @@ png_write_image_8bit(png_voidp argument)
        display->first_row);
    png_bytep output_row = png_voidcast(png_bytep, display->local_row);
    png_uint_32 y = image->height;
-   const unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
+   unsigned int channels = (image->format & PNG_FORMAT_FLAG_COLOR) != 0 ?
        3 : 1;
 
    if ((image->format & PNG_FORMAT_FLAG_ALPHA) != 0)
@@ -1783,25 +1783,25 @@ png_write_image_8bit(png_voidp argument)
 static void
 png_image_set_PLTE(png_image_write_control *display)
 {
-   const png_imagep image = display->image;
+   png_imagep image = display->image;
    const void *cmap = display->colormap;
-   const int entries = image->colormap_entries > 256 ? 256 :
+   int entries = image->colormap_entries > 256 ? 256 :
        (int)image->colormap_entries;
 
    /* NOTE: the caller must check for cmap != NULL and entries != 0 */
-   const png_uint_32 format = image->format;
-   const unsigned int channels = PNG_IMAGE_SAMPLE_CHANNELS(format);
+   png_uint_32 format = image->format;
+   unsigned int channels = PNG_IMAGE_SAMPLE_CHANNELS(format);
 
 #   if defined(PNG_FORMAT_BGR_SUPPORTED) &&\
       defined(PNG_SIMPLIFIED_WRITE_AFIRST_SUPPORTED)
-      const int afirst = (format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
+      int afirst = (format & PNG_FORMAT_FLAG_AFIRST) != 0 &&
           (format & PNG_FORMAT_FLAG_ALPHA) != 0;
 #   else
 #     define afirst 0
 #   endif
 
 #   ifdef PNG_FORMAT_BGR_SUPPORTED
-      const int bgr = (format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
+      int bgr = (format & PNG_FORMAT_FLAG_BGR) != 0 ? 2 : 0;
 #   else
 #     define bgr 0
 #   endif
@@ -1951,12 +1951,12 @@ png_image_write_main(png_voidp argument)
     * and total image size to ensure that they are within the system limits.
     */
    {
-      const unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
+      unsigned int channels = PNG_IMAGE_PIXEL_CHANNELS(image->format);
 
       if (image->width <= 0x7fffffffU/channels) /* no overflow */
       {
          png_uint_32 check;
-         const png_uint_32 png_row_stride = image->width * channels;
+         png_uint_32 png_row_stride = image->width * channels;
 
          if (display->row_stride == 0)
             display->row_stride = (png_int_32)/*SAFE*/png_row_stride;
@@ -2052,7 +2052,7 @@ png_image_write_main(png_voidp argument)
     */
    if (write_16bit != 0)
    {
-      const png_uint_16 le = 0x0001;
+      png_uint_16 le = 0x0001;
 
       if ((*(png_const_bytep) & le) != 0)
          png_set_swap(png_ptr);
@@ -2166,7 +2166,7 @@ image_memory_write)(png_structp png_ptr, png_bytep/*const*/ data, size_t size)
 {
    png_image_write_control *display = png_voidcast(png_image_write_control*,
        png_ptr->io_ptr/*backdoor: png_get_io_ptr(png_ptr)*/);
-   const png_alloc_size_t ob = display->output_bytes;
+   png_alloc_size_t ob = display->output_bytes;
 
    /* Check for overflow; this should never happen: */
    if (size <= ((png_alloc_size_t)-1) - ob)
diff --git a/pngwtran.c b/pngwtran.c
index 9ed551eca..49a13c1e9 100644
--- a/pngwtran.c
+++ b/pngwtran.c
@@ -254,8 +254,7 @@ png_do_shift(png_row_infop row_info, png_bytep row,
 
          for (i = 0; i < istop; i++, bp++)
          {
-
-            const unsigned int c = i%channels;
+            unsigned int c = i%channels;
             int j;
             unsigned int v, out;
 
@@ -283,7 +282,7 @@ png_do_shift(png_row_infop row_info, png_bytep row,
 
          for (bp = row, i = 0; i < istop; i++)
          {
-            const unsigned int c = i%channels;
+            unsigned int c = i%channels;
             int j;
             unsigned int value, v;
 
diff --git a/pngwutil.c b/pngwutil.c
index 5a4ded5f6..16345e4c0 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -2101,7 +2101,7 @@ png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
    static const png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
 
    /* Offset to next interlace block */
-   static const png_byte  png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
+   static const png_byte png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
 
    png_debug(1, "in png_do_write_interlace");
 
@@ -2276,7 +2276,7 @@ png_write_filtered_row(png_structrp png_ptr, png_bytep filtered_row,
 
 #ifdef PNG_WRITE_FILTER_SUPPORTED
 static size_t /* PRIVATE */
-png_setup_sub_row(png_structrp png_ptr, const png_uint_32 bpp,
+png_setup_sub_row(png_structrp png_ptr, png_uint_32 bpp,
     size_t row_bytes, size_t lmins)
 {
    png_bytep rp, dp, lp;
@@ -2315,7 +2315,7 @@ png_setup_sub_row(png_structrp png_ptr, const png_uint_32 bpp,
 }
 
 static void /* PRIVATE */
-png_setup_sub_row_only(png_structrp png_ptr, const png_uint_32 bpp,
+png_setup_sub_row_only(png_structrp png_ptr, png_uint_32 bpp,
     size_t row_bytes)
 {
    png_bytep rp, dp, lp;
@@ -2380,7 +2380,7 @@ png_setup_up_row_only(png_structrp png_ptr, size_t row_bytes)
 }
 
 static size_t /* PRIVATE */
-png_setup_avg_row(png_structrp png_ptr, const png_uint_32 bpp,
+png_setup_avg_row(png_structrp png_ptr, png_uint_32 bpp,
     size_t row_bytes, size_t lmins)
 {
    png_bytep rp, dp, pp, lp;
@@ -2420,7 +2420,7 @@ png_setup_avg_row(png_structrp png_ptr, const png_uint_32 bpp,
    return (sum);
 }
 static void /* PRIVATE */
-png_setup_avg_row_only(png_structrp png_ptr, const png_uint_32 bpp,
+png_setup_avg_row_only(png_structrp png_ptr, png_uint_32 bpp,
     size_t row_bytes)
 {
    png_bytep rp, dp, pp, lp;
@@ -2442,7 +2442,7 @@ png_setup_avg_row_only(png_structrp png_ptr, const png_uint_32 bpp,
 }
 
 static size_t /* PRIVATE */
-png_setup_paeth_row(png_structrp png_ptr, const png_uint_32 bpp,
+png_setup_paeth_row(png_structrp png_ptr, png_uint_32 bpp,
     size_t row_bytes, size_t lmins)
 {
    png_bytep rp, dp, pp, cp, lp;
@@ -2503,7 +2503,7 @@ png_setup_paeth_row(png_structrp png_ptr, const png_uint_32 bpp,
    return (sum);
 }
 static void /* PRIVATE */
-png_setup_paeth_row_only(png_structrp png_ptr, const png_uint_32 bpp,
+png_setup_paeth_row_only(png_structrp png_ptr, png_uint_32 bpp,
     size_t row_bytes)
 {
    png_bytep rp, dp, pp, cp, lp;
diff --git a/powerpc/filter_vsx_intrinsics.c b/powerpc/filter_vsx_intrinsics.c
index 39521cfc8..93656d92d 100644
--- a/powerpc/filter_vsx_intrinsics.c
+++ b/powerpc/filter_vsx_intrinsics.c
@@ -173,7 +173,7 @@ static const vector unsigned char VSX_SHORT_TO_CHAR4_3 = {16,16,16,16,16,16,16,1
 void png_read_filter_row_sub4_vsx(png_row_infop row_info, png_bytep row,
                                   png_const_bytep prev_row)
 {
-   const png_byte bpp = 4;
+   png_byte bpp = 4;
 
    vector unsigned char rp_vec;
    vector unsigned char part_vec;
@@ -230,7 +230,7 @@ void png_read_filter_row_sub4_vsx(png_row_infop row_info, png_bytep row,
 void png_read_filter_row_sub3_vsx(png_row_infop row_info, png_bytep row,
                                   png_const_bytep prev_row)
 {
-   const png_byte bpp = 3;
+   png_byte bpp = 3;
 
    vector unsigned char rp_vec;
    vector unsigned char part_vec;
@@ -294,7 +294,7 @@ void png_read_filter_row_sub3_vsx(png_row_infop row_info, png_bytep row,
 void png_read_filter_row_avg4_vsx(png_row_infop row_info, png_bytep row,
                                   png_const_bytep prev_row)
 {
-   const png_byte bpp = 4;
+   png_byte bpp = 4;
 
    vector unsigned char rp_vec;
    vector unsigned char pp_vec;
@@ -381,7 +381,7 @@ void png_read_filter_row_avg4_vsx(png_row_infop row_info, png_bytep row,
 void png_read_filter_row_avg3_vsx(png_row_infop row_info, png_bytep row,
                                   png_const_bytep prev_row)
 {
-  const png_byte bpp = 3;
+  png_byte bpp = 3;
 
   vector unsigned char rp_vec;
   vector unsigned char pp_vec;
@@ -499,7 +499,7 @@ void png_read_filter_row_avg3_vsx(png_row_infop row_info, png_bytep row,
 void png_read_filter_row_paeth4_vsx(png_row_infop row_info, png_bytep row,
    png_const_bytep prev_row)
 {
-   const png_byte bpp = 4;
+   png_byte bpp = 4;
 
    int a, b, c, pa, pb, pc, p;
    vector unsigned char rp_vec;
@@ -619,7 +619,7 @@ void png_read_filter_row_paeth4_vsx(png_row_infop row_info, png_bytep row,
 void png_read_filter_row_paeth3_vsx(png_row_infop row_info, png_bytep row,
    png_const_bytep prev_row)
 {
-  const png_byte bpp = 3;
+  png_byte bpp = 3;
 
   int a, b, c, pa, pb, pc, p;
   vector unsigned char rp_vec;