diff --git a/ANNOUNCE b/ANNOUNCE
index b888474e4..90d40ac85 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.6.0beta33 - December 13, 2012
+Libpng 1.6.0beta33 - December 15, 2012
 
 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.
@@ -552,7 +552,7 @@ Version 1.6.0beta32 [November 25, 2012]
   Fixed error checking in the simplified write API (Olaf van der Spek)
   Made png_user_version_check() ok to use with libpng version 1.10.x and later.
 
-Version 1.6.0beta33 [December 13, 2012]
+Version 1.6.0beta33 [December 15, 2012]
   Fixed typo in png.c (PNG_SET_CHUNK_MALLOC_MAX should be PNG_CHUNK_MALLOC_MAX)
     that causes the MALLOC_MAX limit not to work (John Bowler)
   Change png_warning() to png_app_error() in pngwrite.c and comment the
diff --git a/CHANGES b/CHANGES
index 0ce1c7ef0..bda6f2573 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4304,7 +4304,8 @@ Version 1.6.0beta32 [November 25, 2012]
   Fixed error checking in the simplified write API (Olaf van der Spek)
   Made png_user_version_check() ok to use with libpng version 1.10.x and later.
 
-Version 1.6.0beta33 [December 13, 2012]
+  Fixed cases of unquoted DESTDIR in Makefile.am
+Version 1.6.0beta33 [December 15, 2012]
   Fixed typo in png.c (PNG_SET_CHUNK_MALLOC_MAX should be PNG_CHUNK_MALLOC_MAX)
     that causes the MALLOC_MAX limit not to work (John Bowler)
   Change png_warning() to png_app_error() in pngwrite.c and comment the
diff --git a/arm/arm_init.c b/arm/arm_init.c
index 6b0a925f2..8925f352f 100644
--- a/arm/arm_init.c
+++ b/arm/arm_init.c
@@ -1,8 +1,9 @@
 
-/* filter_neon.S - NEON optimised filter functions
+/* arm_init.c - NEON optimised filter functions
  *
- * Copyright (c) 2011 Glenn Randers-Pehrson
+ * Copyright (c) 2012 Glenn Randers-Pehrson
  * Written by Mans Rullgard, 2011.
+ * Last changed in libpng 1.5.14 [(PENDING RELEASE)]
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
@@ -50,6 +51,17 @@ png_init_filter_functions_neon(png_structp pp, unsigned int bpp)
       return;
 #endif
 
+   /* IMPORTANT: any new external functions used here must be declared using
+    * PNG_INTERNAL_FUNCTION in ../pngpriv.h.  This is required so that the
+    * 'prefix' option to configure works:
+    *
+    *    ./configure --with-libpng-prefix=foobar_
+    *
+    * Verify you have got this right by running the above command, doing a build
+    * and examining pngprefix.h; it must contain a #define for every external
+    * function you add.  (Notice that this happens automatically for the
+    * initialization function.)
+    */
    pp->read_filter[PNG_FILTER_VALUE_UP-1] = png_read_filter_row_up_neon;
 
    if (bpp == 3)
diff --git a/arm/filter_neon.S b/arm/filter_neon.S
index 9ce04d3be..4aa500cd7 100644
--- a/arm/filter_neon.S
+++ b/arm/filter_neon.S
@@ -3,6 +3,7 @@
  *
  * Copyright (c) 2011 Glenn Randers-Pehrson
  * Written by Mans Rullgard, 2011.
+ * Last changed in libpng 1.5.7 [December 15, 2011]
  *
  * This code is released under the libpng license.
  * For conditions of distribution and use, see the disclaimer
diff --git a/pngrutil.c b/pngrutil.c
index db7afb315..6e613c012 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -3865,6 +3865,14 @@ png_read_filter_row_paeth_multibyte_pixel(png_row_infop row_info, png_bytep row,
 
 static void
 png_init_filter_functions(png_structrp pp)
+   /* This function is called once for every PNG image to set the
+    * implementations required to reverse the filtering of PNG rows.  Reversing
+    * the filter is the first transformation performed on the row data.  It is
+    * performed in place, therefore an implementation can be selected based on
+    * the image pixel format.  If the implementation depends on image width then
+    * take care to ensure that it works corretly if the image is interlaced -
+    * interlacing causes the actual row width to vary.
+    */
 {
    unsigned int bpp = (pp->pixel_depth + 7) >> 3;
 
@@ -3895,6 +3903,10 @@ void /* PRIVATE */
 png_read_filter_row(png_structrp pp, png_row_infop row_info, png_bytep row,
    png_const_bytep prev_row, int filter)
 {
+   /* OPTIMIZATION: DO NOT MODIFY THIS FUNCTION, instead #define
+    * PNG_FILTER_OPTIMIZATIONS to a function that overrides the generic
+    * implementations.  See png_init_filter_functions above.
+    */
    if (pp->read_filter[0] == NULL)
       png_init_filter_functions(pp);
    if (filter > PNG_FILTER_VALUE_NONE && filter < PNG_FILTER_VALUE_LAST)