diff --git a/ANNOUNCE b/ANNOUNCE
index a5230daf7..0bf620bb6 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.6.0beta23 - June 4, 2012
+Libpng 1.6.0beta23 - June 6, 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.
@@ -369,13 +369,16 @@ Version 1.6.0beta22 [May 23, 2012]
     introducing new png_aligncast macros to do the cast in a way that clang
     accepts.
 
-Version 1.6.0beta23 [June 4, 2012]
+Version 1.6.0beta23 [June 6, 2012]
   Revised CMakeLists.txt to not attempt to make a symlink under mingw.
   Made fixes for new optimization warnings from gcc 4.7.0. The compiler
     performs an optimization which is safe; however it then warns about it.
     Changing the type of 'palette_number' in pngvalid.c removes the warning.
   Do not depend upon a GCC feature macro being available for use in generating
     the linker mapfile symbol prefix.
+  Improved performance of new do_check_palette_indexes() function (only
+    update the value when it actually increases, move test for whether
+    the check is wanted out of the function.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 1b16cf213..c6f718098 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4120,13 +4120,16 @@ Version 1.6.0beta22 [May 23, 2012]
     introducing new png_aligncast macros to do the cast in a way that clang
     accepts.
 
-Version 1.6.0beta23 [June 4, 2012]
+Version 1.6.0beta23 [June 6, 2012]
   Revised CMakeLists.txt to not attempt to make a symlink under mingw.
   Made fixes for new optimization warnings from gcc 4.7.0. The compiler
     performs an optimization which is safe; however it then warns about it.
     Changing the type of 'palette_number' in pngvalid.c removes the warning.
   Do not depend upon a GCC feature macro being available for use in generating
     the linker mapfile symbol prefix.
+  Improved performance of new do_check_palette_indexes() function (only
+    update the value when it actually increases, move test for whether
+    the check is wanted out of the function.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngrtran.c b/pngrtran.c
index ef4eca1d1..ce530506f 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -2342,7 +2342,8 @@ png_do_read_transformations(png_structrp png_ptr, png_row_infop row_info)
 
 #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
    /* Added at libpng-1.5.10 */
-   if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
+   if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
+       png_ptr->num_palette_max >= 0)
       png_do_check_palette_indexes(png_ptr, row_info);
 #endif
 
diff --git a/pngtrans.c b/pngtrans.c
index 9a6c1d20d..1d4bf6122 100644
--- a/pngtrans.c
+++ b/pngtrans.c
@@ -625,8 +625,7 @@ png_do_bgr(png_row_infop row_info, png_bytep row)
 void /* PRIVATE */
 png_do_check_palette_indexes(png_structrp png_ptr, png_row_infop row_info)
 {
-   if (png_ptr->num_palette < (1 << row_info->bit_depth) &&
-      png_ptr->num_palette_max >= 0)
+   if (png_ptr->num_palette < (1 << row_info->bit_depth))
    {
       /* Calculations moved outside switch in an attempt to stop different
        * compiler warnings.  'padding' is in *bits* within the last byte, it is
@@ -708,7 +707,7 @@ png_do_check_palette_indexes(png_structrp png_ptr, png_row_infop row_info)
          {
             for (; rp > png_ptr->row_buf; rp--)
             {
-               if (*rp >= png_ptr->num_palette_max)
+               if (*rp > png_ptr->num_palette_max)
                   png_ptr->num_palette_max = (int) *rp;
             }
 
diff --git a/pngwrite.c b/pngwrite.c
index 769da73ba..d206ab078 100644
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -813,7 +813,8 @@ png_write_row(png_structrp png_ptr, png_const_bytep row)
 /* Added at libpng-1.5.10 */
 #ifdef PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED
    /* Check for out-of-range palette index */
-   if(row_info.color_type == PNG_COLOR_TYPE_PALETTE)
+   if (row_info.color_type == PNG_COLOR_TYPE_PALETTE &&
+       png_ptr->num_palette_max >= 0)
       png_do_check_palette_indexes(png_ptr, &row_info);
 #endif