diff --git a/ANNOUNCE b/ANNOUNCE
index c49ead034..69cfb7fa8 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -694,6 +694,7 @@ version 1.4.0beta102 [November 18, 2009]
 
 version 1.4.0beta103 [November 21, 2009]
   Removed obsolete comments about ASM from projects/visualc71/README_zlib.txt
+  Align row_buf on 16-byte boundary in memory.
   Restored the PNG_WRITE_FLUSH_AFTER_IEND guard around the call to png_flush()
     after png_write_IEND().  See 1.4.0beta32, 1.4.0beta50 changes above
     and 1.2.30, 1.2.30rc01 and rc03 in 1.2.41 CHANGES.  Someone needs this
diff --git a/CHANGES b/CHANGES
index 9a5ff997c..7a3e45682 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2381,6 +2381,7 @@ version 1.4.0beta102 [November 18, 2009]
 
 version 1.4.0beta103 [November 21, 2009]
   Removed obsolete comments about ASM from projects/visualc71/README_zlib.txt
+  Align row_buf on 16-byte boundary in memory.
   Restored the PNG_WRITE_FLUSH_AFTER_IEND_SUPPORTED guard around the call
     to png_flush() after png_write_IEND().  See 1.4.0beta32, 1.4.0beta50
     changes above and 1.2.30, 1.2.30rc01 and rc03 in 1.2.41 CHANGES.  Someone
diff --git a/pngrutil.c b/pngrutil.c
index 2ca594864..29425afdb 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -1,7 +1,7 @@
 
 /* pngrutil.c - utilities to read a PNG file
  *
- * Last changed in libpng 1.4.0 [November 20, 2009]
+ * Last changed in libpng 1.4.0 [November 21, 2009]
  * Copyright (c) 1998-2009 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.)
@@ -3281,15 +3281,26 @@ defined(PNG_USER_TRANSFORM_PTR_SUPPORTED)
       png_error(png_ptr, "This image requires a row greater than 64KB");
 #endif
 
-   if (row_bytes + 64 > png_ptr->old_big_row_buf_size)
+   if (row_bytes + 48 > png_ptr->old_big_row_buf_size)
    {
      png_free(png_ptr, png_ptr->big_row_buf);
+     png_ptr->big_row_buf = (png_bytep)png_malloc(png_ptr, row_bytes + 48);
      if (png_ptr->interlaced)
-        png_ptr->big_row_buf = (png_bytep)png_calloc(png_ptr, row_bytes + 64);
-     else
-        png_ptr->big_row_buf = (png_bytep)png_malloc(png_ptr, row_bytes + 64);
+       png_memset(png_ptr->big_row_buf, 0, row_bytes + 48);
+     png_ptr->old_big_row_buf_size = row_bytes + 48;
+
+#ifdef PNG_ALIGNED_MEMORY_SUPPORTED
+     /* Use 16-byte aligned memory for row_buf with at least 16 bytes
+      * of padding before and after row_buf.
+      */
+     png_ptr->row_buf = png_ptr->big_row_buf + 32
+         - (((png_alloc_size_t)&(png_ptr->big_row_buf[0]) + 15) % 16);
+     png_ptr->old_big_row_buf_size = row_bytes + 48;
+#else
+     /* Use 32 bytes of padding before and 16 bytes after row_buf. */
      png_ptr->row_buf = png_ptr->big_row_buf + 32;
-     png_ptr->old_big_row_buf_size = row_bytes + 64;
+#endif
+     png_ptr->old_big_row_buf_size = row_bytes + 48;
    }
 
 #ifdef PNG_MAX_MALLOC_64K