diff --git a/ANNOUNCE b/ANNOUNCE
index 0659ae39d..c4b600e47 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,60 +1,35 @@
 
-Libpng 1.5.2 - March 31, 2011
+Libpng 1.5.3beta01 - April 1, 2011
 
-This is a public release of libpng, intended for use in production codes.
+This is not intended to be a public release.  It will be replaced
+within a few weeks by a public version or by another test version.
 
 Files available for download:
 
 Source files with LF line endings (for Unix/Linux) and with a
 "configure" script
 
-   libpng-1.5.2.tar.xz (LZMA-compressed, recommended)
-   libpng-1.5.2.tar.gz
-   libpng-1.5.2.tar.bz2
+   1.5.3beta01.tar.xz (LZMA-compressed, recommended)
+   1.5.3beta01.tar.gz
+   1.5.3beta01.tar.bz2
 
 Source files with CRLF line endings (for Windows), without the
 "configure" script
 
-   lpng152.7z  (LZMA-compressed, recommended)
-   lpng152.zip
+   lp153b01.7z  (LZMA-compressed, recommended)
+   lp153b01.zip
 
 Other information:
 
-   libpng-1.5.2-README.txt
-   libpng-1.5.2-LICENSE.txt
+   1.5.3beta01-README.txt
+   1.5.3beta01-LICENSE.txt
 
 Changes since the last public release (1.5.2):
 
-  More -Wshadow fixes for older gcc compilers.  Older gcc versions apparently
-    check formal parameters names in function declarations (as well as
-    definitions) to see if they match a name in the global namespace.
-  Revised PNG_EXPORTA macro to not use an empty parameter, to accommodate the
-    old VisualC++ preprocessor.
-  Turned on interlace handling in png_read_png().
-  Fixed gcc pendantic warnings.
-  Handle longjmp in Cygwin.
-  Fixed png_get_current_row_number() in the interlaced case.
-  Cleaned up ALPHA flags and transformations.
-  Implemented expansion to 16 bits.
-  Fixed mistake in the descriptions of user read_transform and write_transform
-    function prototypes in the manual.  The row_info struct is png_row_infop.
-  Corrected png_get_current_row_number documentation
-  Fixed the read/write row callback documentation.
-    This documents the current behavior, where the callback is called after
-    every row with information pertaining to the next row.
-  Fixed scripts/makefile.vcwin32
-  Updated contrib/pngsuite/README to add the word "modify".
-  Define PNG_ALLOCATED and other attributes to blank when _MSC_VER<1300.
-  ifdef out mask arrays in pngread.c when interlacing is not supported.
-  Added a hint to try CPP=/bin/cpp if "cpp -E" fails in scripts/pnglibconf.mak
-    and in contrib/pngminim/*/makefile, eg., on SunOS 5.10, and removed "strip"
-    from the makefiles.
-  Fixed a bug (present since libpng-1.0.7) that makes png_handle_sPLT() fail
-    to compile when PNG_NO_POINTER_INDEXING is defined (Chubanov Kirill)
-  Don't include standard header files in png.h while building the symbol table,
-    to avoid cpp failure on SunOS (introduced PNG_BUILDING_SYMBOL_TABLE macro).
+Version 1.5.3beta01 [April 1, 2011]
+  Re-initialize the zlib compressor before compressing non-IDAT chunks.
 
-Send comments/corrections/commendations to png-mng-implement at lists.sf.net
+Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
 (subscription required; visit
 https://lists.sourceforge.net/lists/listinfo/png-mng-implement
 to subscribe) or to glennrp at users.sourceforge.net
diff --git a/CHANGES b/CHANGES
index fb069121a..f9be127eb 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3285,6 +3285,10 @@ Version 1.5.2rc03 [March 24, 2011]
     to avoid cpp failure on SunOS (introduced PNG_BUILDING_SYMBOL_TABLE macro).
 
 Version 1.5.2 [March 31, 2011]
+  No changes.
+
+Version 1.5.3beta01 [April 1, 2011]
+  Re-initialize the zlib compressor before compressing non-IDAT chunks.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/png.h b/png.h
index 0af42b170..0601f4728 100644
--- a/png.h
+++ b/png.h
@@ -1,7 +1,7 @@
 
 /* png.h - header file for PNG reference library
  *
- * libpng version 1.5.2 - March 31, 2011
+ * libpng version 1.5.3beta01 - April 1, 2011
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -11,7 +11,7 @@
  * Authors and maintainers:
  *   libpng versions 0.71, May 1995, through 0.88, January 1996: Guy Schalnat
  *   libpng versions 0.89c, June 1996, through 0.96, May 1997: Andreas Dilger
- *   libpng versions 0.97, January 1998, through 1.5.2 - March 31, 2011: Glenn
+ *   libpng versions 0.97, January 1998, through 1.5.3beta01 - April 1, 2011: Glenn
  *   See also "Contributing Authors", below.
  *
  * Note about libpng version numbers:
@@ -181,7 +181,7 @@
  *
  * This code is released under the libpng license.
  *
- * libpng versions 1.2.6, August 15, 2004, through 1.5.2, March 31, 2011, are
+ * libpng versions 1.2.6, August 15, 2004, through 1.5.3beta01, April 1, 2011, are
  * Copyright (c) 2004, 2006-2011 Glenn Randers-Pehrson, and are
  * distributed according to the same disclaimer and license as libpng-1.2.5
  * with the following individual added to the list of Contributing Authors:
@@ -293,13 +293,13 @@
  * Y2K compliance in libpng:
  * =========================
  *
- *    March 31, 2011
+ *    April 1, 2011
  *
  *    Since the PNG Development group is an ad-hoc body, we can't make
  *    an official declaration.
  *
  *    This is your unofficial assurance that libpng from version 0.71 and
- *    upward through 1.5.2 are Y2K compliant.  It is my belief that
+ *    upward through 1.5.3beta01 are Y2K compliant.  It is my belief that
  *    earlier versions were also Y2K compliant.
  *
  *    Libpng only has three year fields.  One is a 2-byte unsigned integer
@@ -355,9 +355,9 @@
  */
 
 /* Version information for png.h - this should match the version in png.c */
-#define PNG_LIBPNG_VER_STRING "1.5.2"
+#define PNG_LIBPNG_VER_STRING "1.5.3beta01"
 #define PNG_HEADER_VERSION_STRING \
-     " libpng version 1.5.2 - March 31, 2011\n"
+     " libpng version 1.5.3beta01 - April 1, 2011\n"
 
 #define PNG_LIBPNG_VER_SONUM   15
 #define PNG_LIBPNG_VER_DLLNUM  15
@@ -365,12 +365,12 @@
 /* These should match the first 3 components of PNG_LIBPNG_VER_STRING: */
 #define PNG_LIBPNG_VER_MAJOR   1
 #define PNG_LIBPNG_VER_MINOR   5
-#define PNG_LIBPNG_VER_RELEASE 2
+#define PNG_LIBPNG_VER_RELEASE 3
 /* This should match the numeric part of the final component of
  * PNG_LIBPNG_VER_STRING, omitting any leading zero:
  */
 
-#define PNG_LIBPNG_VER_BUILD  0
+#define PNG_LIBPNG_VER_BUILD  01
 
 /* Release Status */
 #define PNG_LIBPNG_BUILD_ALPHA    1
@@ -395,7 +395,7 @@
  * version 1.0.0 was mis-numbered 100 instead of 10000).  From
  * version 1.0.1 it's    xxyyzz, where x=major, y=minor, z=release
  */
-#define PNG_LIBPNG_VER 10502 /* 1.5.2 */
+#define PNG_LIBPNG_VER 10503 /* 1.5.3 */
 
 /* Library configuration: these options cannot be changed after
  * the library has been built.
@@ -517,7 +517,7 @@ extern "C" {
 /* This triggers a compiler error in png.c, if png.c and png.h
  * do not agree upon the version number.
  */
-typedef char* png_libpng_version_1_5_2;
+typedef char* png_libpng_version_1_5_3beta01;
 
 /* Three color definitions.  The order of the red, green, and blue, (and the
  * exact size) is not important, although the size of the fields need to
@@ -1413,6 +1413,24 @@ PNG_EXPORT(72, void, png_set_compression_window_bits, (png_structp png_ptr,
 PNG_EXPORT(73, void, png_set_compression_method, (png_structp png_ptr,
     int method));
 
+#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION
+/* Also set zlib parameters for compressing non-IDAT chunks */
+PNG_EXPORT(222, void, png_set_text_compression_level,
+    (png_structp png_ptr, int level));
+
+PNG_EXPORT(223, void, png_set_text_compression_mem_level, (png_structp png_ptr,
+    int mem_level));
+
+PNG_EXPORT(224, void, png_set_text_compression_strategy, (png_structp png_ptr,
+    int strategy));
+
+PNG_EXPORT(225, void, png_set_text_compression_window_bits, (png_structp
+    png_ptr, int window_bits));
+
+PNG_EXPORT(226, void, png_set_text_compression_method, (png_structp png_ptr,
+    int method));
+#endif /* PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
+
 /* These next functions are called for input/output, memory, and error
  * handling.  They are in the file pngrio.c, pngwio.c, and pngerror.c,
  * and call standard C I/O routines such as fread(), fwrite(), and
diff --git a/pngconf.h b/pngconf.h
index c82fa5866..c355573d9 100644
--- a/pngconf.h
+++ b/pngconf.h
@@ -1,7 +1,7 @@
 
 /* pngconf.h - machine configurable file for libpng
  *
- * libpng version 1.5.2 - March 31, 2011
+ * libpng version 1.5.3beta01 - March 31, 2011
  *
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
diff --git a/pngmem.c b/pngmem.c
index a15d8b085..487c96bec 100644
--- a/pngmem.c
+++ b/pngmem.c
@@ -187,8 +187,9 @@ png_malloc_default,(png_structp png_ptr, png_alloc_size_t size),PNG_ALLOCATED)
             int num_blocks;
             png_uint_32 total_size;
             png_bytep table;
-            int i;
+            int i, mem_level, window_bits;
             png_byte huge * hptr;
+            int window_bits
 
             if (ret != NULL)
             {
@@ -196,14 +197,22 @@ png_malloc_default,(png_structp png_ptr, png_alloc_size_t size),PNG_ALLOCATED)
                ret = NULL;
             }
 
-            if (png_ptr->zlib_window_bits > 14)
-               num_blocks = (int)(1 << (png_ptr->zlib_window_bits - 14));
+            window_bits =
+                png_ptr->zlib_window_bits >= png_ptr->zlib_text_window_bits ?
+                png_ptr->zlib_window_bits : png_ptr->zlib_text_window_bits;
+
+            if (window_bits > 14)
+               num_blocks = (int)(1 << (window_bits - 14));
 
             else
                num_blocks = 1;
 
-            if (png_ptr->zlib_mem_level >= 7)
-               num_blocks += (int)(1 << (png_ptr->zlib_mem_level - 7));
+            mem_level =
+                png_ptr->zlib_mem_level >= png_ptr->zlib_text_mem_level ?
+                png_ptr->zlib_mem_level : png_ptr->zlib_text_mem_level;
+
+            if (mem_level >= 7)
+               num_blocks += (int)(1 << (mem_level - 7));
 
             else
                num_blocks++;
@@ -277,7 +286,7 @@ png_malloc_default,(png_structp png_ptr, png_alloc_size_t size),PNG_ALLOCATED)
       {
 #  ifndef PNG_USER_MEM_SUPPORTED
          if ((png_ptr->flags&PNG_FLAG_MALLOC_NULL_MEM_OK) == 0)
-            png_error(png_ptr, "Out of Memory"); /* Note "o" and "M" */
+            png_error(png_ptr, "Out of Memory"); /* Note "O" and "M" */
 
          else
             png_warning(png_ptr, "Out of Memory");
diff --git a/pngpriv.h b/pngpriv.h
index a7e3b5272..5bc4f38a6 100644
--- a/pngpriv.h
+++ b/pngpriv.h
@@ -345,13 +345,13 @@ typedef PNG_CONST png_uint_16p FAR * png_const_uint_16pp;
                                   /*      0x200000L  unused */
                                   /*      0x400000L  unused */
 #define PNG_FLAG_BENIGN_ERRORS_WARN       0x800000L  /* Added to libpng-1.4.0 */
-                                  /*     0x1000000L  unused */
-                                  /*     0x2000000L  unused */
-                                  /*     0x4000000L  unused */
-                                  /*     0x8000000L  unused */
-                                  /*    0x10000000L  unused */
-                                  /*    0x20000000L  unused */
-                                  /*    0x40000000L  unused */
+#define PNG_FLAG_ZTXT_CUSTOM_STRATEGY    0x1000000L  /* 5 lines added */
+#define PNG_FLAG_ZTXT_CUSTOM_LEVEL       0x2000000L  /* to libpng-1.5.2 */
+#define PNG_FLAG_ZTXT_CUSTOM_MEM_LEVEL   0x4000000L
+#define PNG_FLAG_ZTXT_CUSTOM_WINDOW_BITS 0x8000000L
+#define PNG_FLAG_ZTXT_CUSTOM_METHOD      0x10000000L
+                                  /*     0x20000000L  unused */
+                                  /*     0x40000000L  unused */
 
 #define PNG_FLAG_CRC_ANCILLARY_MASK (PNG_FLAG_CRC_ANCILLARY_USE | \
                                      PNG_FLAG_CRC_ANCILLARY_NOWARN)
diff --git a/pngstruct.h b/pngstruct.h
index 8d781faef..47d65be82 100644
--- a/pngstruct.h
+++ b/pngstruct.h
@@ -69,6 +69,13 @@ struct png_struct_def
    int zlib_window_bits;      /* holds zlib compression window bits */
    int zlib_mem_level;        /* holds zlib compression memory level */
    int zlib_strategy;         /* holds zlib compression strategy */
+/* Added at libpng 1.5.2 */
+   int zlib_text_level;            /* holds zlib compression level */
+   int zlib_text_method;           /* holds zlib compression method */
+   int zlib_text_window_bits;      /* holds zlib compression window bits */
+   int zlib_text_mem_level;        /* holds zlib compression memory level */
+   int zlib_text_strategy;         /* holds zlib compression strategy */
+/* End of material added at libpng 1.5.2 */
 
    png_uint_32 width;         /* width of image in pixels */
    png_uint_32 height;        /* height of image in pixels */
diff --git a/pngwrite.c b/pngwrite.c
index 9277a9516..c7611ee9b 100644
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -1,7 +1,7 @@
 
 /* pngwrite.c - general routines to write a PNG file
  *
- * Last changed in libpng 1.5.1 [February 3, 2011]
+ * Last changed in libpng 1.5.3 [(PENDING RELEASE)]
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -1491,6 +1491,86 @@ png_set_compression_method(png_structp png_ptr, int method)
    png_ptr->zlib_method = method;
 }
 
+/* The following were added to libpng-1.5.2 */
+#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION
+void PNGAPI
+png_set_text_compression_level(png_structp png_ptr, int level)
+{
+   png_debug(1, "in png_set_text_compression_level");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->flags |= PNG_FLAG_ZTXT_CUSTOM_LEVEL;
+   png_ptr->zlib_text_level = level;
+}
+
+void PNGAPI
+png_set_text_compression_mem_level(png_structp png_ptr, int mem_level)
+{
+   png_debug(1, "in png_set_text_compression_mem_level");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->flags |= PNG_FLAG_ZTXT_CUSTOM_MEM_LEVEL;
+   png_ptr->zlib_text_mem_level = mem_level;
+}
+
+void PNGAPI
+png_set_text_compression_strategy(png_structp png_ptr, int strategy)
+{
+   png_debug(1, "in png_set_text_compression_strategy");
+
+   if (png_ptr == NULL)
+      return;
+
+   png_ptr->flags |= PNG_FLAG_ZTXT_CUSTOM_STRATEGY;
+   png_ptr->zlib_text_strategy = strategy;
+}
+
+void PNGAPI
+png_set_text_compression_window_bits(png_structp png_ptr, int window_bits)
+{
+   if (png_ptr == NULL)
+      return;
+
+   if (window_bits > 15)
+      png_warning(png_ptr, "Only compression windows <= 32k supported by PNG");
+
+   else if (window_bits < 8)
+      png_warning(png_ptr, "Only compression windows >= 256 supported by PNG");
+
+#ifndef WBITS_8_OK
+   /* Avoid libpng bug with 256-byte windows */
+   if (window_bits == 8)
+      {
+        png_warning(png_ptr, "Text compression window is being reset to 512");
+        window_bits = 9;
+      }
+
+#endif
+   png_ptr->flags |= PNG_FLAG_ZTXT_CUSTOM_WINDOW_BITS;
+   png_ptr->zlib_text_window_bits = window_bits;
+}
+
+void PNGAPI
+png_set_text_compression_method(png_structp png_ptr, int method)
+{
+   png_debug(1, "in png_set_text_compression_method");
+
+   if (png_ptr == NULL)
+      return;
+
+   if (method != 8)
+      png_warning(png_ptr, "Only compression method 8 is supported by PNG");
+
+   png_ptr->flags |= PNG_FLAG_ZTXT_CUSTOM_METHOD;
+   png_ptr->zlib_text_method = method;
+}
+#endif /* PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
+/* end of API added to libpng-1.5.2 */
+
 void PNGAPI
 png_set_write_status_fn(png_structp png_ptr, png_write_status_ptr write_row_fn)
 {
diff --git a/pngwutil.c b/pngwutil.c
index 2c35785aa..44ef005b4 100644
--- a/pngwutil.c
+++ b/pngwutil.c
@@ -1,7 +1,7 @@
 
 /* pngwutil.c - utilities to write a PNG file
  *
- * Last changed in libpng 1.5.0 [January 6, 2011]
+ * Last changed in libpng 1.5.3 [(PENDING RELEASE)]
  * Copyright (c) 1998-2011 Glenn Randers-Pehrson
  * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
  * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
@@ -256,9 +256,33 @@ png_text_compress(png_structp png_ptr,
     * wouldn't cause a failure, just a slowdown due to swapping).
     */
 
+   /* Initialize the compressor.  To do: Why do we need this? */
+   ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_text_level,
+       png_ptr->zlib_text_method, png_ptr->zlib_text_window_bits,
+       png_ptr->zlib_text_mem_level, png_ptr->zlib_text_strategy);
+
+   if (ret != Z_OK)
+   {
+      if (ret == Z_VERSION_ERROR)
+         png_error(png_ptr,
+            "zlib failed to initialize compressor for text-- version error");
+
+      if (ret == Z_STREAM_ERROR)
+         png_error(png_ptr,
+             "zlib failed to initialize compressor for text-- stream error");
+
+      if (ret == Z_MEM_ERROR)
+         png_error(png_ptr,
+             "zlib failed to initialize compressor for text-- mem error");
+
+      png_error(png_ptr, "zlib failed to initialize compressor for text");
+   }
+
    /* Set up the compression buffers */
+
    /* TODO: the following cast hides a potential overflow problem. */
    png_ptr->zstream.avail_in = (uInt)text_len;
+
    /* NOTE: assume zlib doesn't overwrite the input */
    png_ptr->zstream.next_in = (Bytef *)text;
    png_ptr->zstream.avail_out = png_ptr->zbuf_size;
@@ -437,7 +461,6 @@ png_write_compressed_data_out(png_structp png_ptr, compression_state *comp)
 
    /* Reset zlib for another zTXt/iTXt or image data */
    deflateReset(&png_ptr->zstream);
-   png_ptr->zstream.data_type = Z_BINARY;
 }
 #endif
 
@@ -632,34 +655,34 @@ png_write_IHDR(png_structp png_ptr, png_uint_32 width, png_uint_32 height,
    if (!(png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_METHOD))
       png_ptr->zlib_method = 8;
 
+#ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_STRATEGY))
+      png_ptr->zlib_text_strategy = Z_DEFAULT_STRATEGY;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_LEVEL))
+      png_ptr->zlib_text_level = Z_DEFAULT_COMPRESSION;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_MEM_LEVEL))
+      png_ptr->zlib_text_mem_level = 8;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_WINDOW_BITS))
+      png_ptr->zlib_text_window_bits = 15;
+
+   if (!(png_ptr->flags & PNG_FLAG_ZTXT_CUSTOM_METHOD))
+      png_ptr->zlib_text_method = 8;
+#else
+   png_ptr->zlib_text_strategy = Z_DEFAULT_STRATEGY;
+   png_ptr->zlib_text_level = Z_DEFAULT_COMPRESSION;
+   png_ptr->zlib_text_mem_level = 8;
+   png_ptr->zlib_text_window_bits = 15;
+   png_ptr->zlib_text_method = 8;
+#endif /* PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION */
+
+   /* Initialize the zlib compressor */
    ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
        png_ptr->zlib_method, png_ptr->zlib_window_bits,
        png_ptr->zlib_mem_level, png_ptr->zlib_strategy);
 
-   if (ret != Z_OK)
-   {
-      if (ret == Z_VERSION_ERROR)
-         png_error(png_ptr,
-            "zlib failed to initialize compressor -- version error");
-
-      if (ret == Z_STREAM_ERROR)
-         png_error(png_ptr,
-             "zlib failed to initialize compressor -- stream error");
-
-      if (ret == Z_MEM_ERROR)
-         png_error(png_ptr,
-             "zlib failed to initialize compressor -- mem error");
-
-      png_error(png_ptr, "zlib failed to initialize compressor");
-   }
-
-   png_ptr->zstream.next_out = png_ptr->zbuf;
-   png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
-   /* libpng is not interested in zstream.data_type, so set it
-    * to a predefined value, to avoid its evaluation inside zlib
-    */
-   png_ptr->zstream.data_type = Z_BINARY;
-
    png_ptr->mode = PNG_HAVE_IHDR;
 }
 
@@ -750,7 +773,39 @@ png_write_IDAT(png_structp png_ptr, png_bytep data, png_size_t length)
    if (!(png_ptr->mode & PNG_HAVE_IDAT) &&
        png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
    {
-      unsigned int z_cmf = data[0];  /* zlib compression method and flags */
+      int ret;
+      unsigned int z_cmf;  /* zlib compression method and flags */
+
+      ret = deflateInit2(&png_ptr->zstream, png_ptr->zlib_level,
+          png_ptr->zlib_method, png_ptr->zlib_window_bits,
+          png_ptr->zlib_mem_level, png_ptr->zlib_strategy);
+
+      if (ret != Z_OK)
+      {
+         if (ret == Z_VERSION_ERROR)
+            png_error(png_ptr,
+               "zlib failed to initialize compressor -- version error");
+
+         if (ret == Z_STREAM_ERROR)
+            png_error(png_ptr,
+                "zlib failed to initialize compressor -- stream error");
+
+         if (ret == Z_MEM_ERROR)
+            png_error(png_ptr,
+                "zlib failed to initialize compressor -- mem error");
+
+         png_error(png_ptr, "zlib failed to initialize compressor");
+      }
+
+      png_ptr->zstream.next_out = png_ptr->zbuf;
+      png_ptr->zstream.avail_out = (uInt)png_ptr->zbuf_size;
+      /* libpng is not interested in zstream.data_type, so set it
+       * to a predefined value, to avoid its evaluation inside zlib
+       */
+      png_ptr->zstream.data_type = Z_BINARY;
+
+      z_cmf = data[0];
+
       if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
       {
          /* Avoid memory underflows and multiplication overflows.