diff --git a/ANNOUNCE b/ANNOUNCE
index 0c4f18306..99d4d8bbb 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.5.11rc04 - June 4, 2012
+Libpng 1.5.11rc04 - 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.
@@ -54,7 +54,8 @@ Version 1.5.11rc03 [June 4, 2012]
     performs an optimization which is safe; however it then warns about it.
     Changing the type of 'palette_number' in pngvalid.c removes the warning.
 
-Version 1.5.11rc04 [June 4, 2012]
+Version 1.5.11rc04 [June 6, 2012]
+  Improved efficiency of new do_check_palette_indexes() function.
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net:
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index 721538993..80a6766f5 100644
--- a/CHANGES
+++ b/CHANGES
@@ -3882,7 +3882,8 @@ Version 1.5.11rc03 [June 4, 2012]
     performs an optimization which is safe; however it then warns about it.
     Changing the type of 'palette_number' in pngvalid.c removes the warning.
 
-Version 1.5.11rc04 [June 4, 2012]
+Version 1.5.11rc04 [June 6, 2012]
+  Improved performance of new do_check_palette_indexes() 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 556185286..906cb52f1 100644
--- a/pngrtran.c
+++ b/pngrtran.c
@@ -2301,7 +2301,8 @@ png_do_read_transformations(png_structp 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 fef12f185..44e8bc6d8 100644
--- a/pngtrans.c
+++ b/pngtrans.c
@@ -708,7 +708,7 @@ png_do_check_palette_indexes(png_structp 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 b587f1b99..d0567d84e 100644
--- a/pngwrite.c
+++ b/pngwrite.c
@@ -806,7 +806,8 @@ png_write_row(png_structp 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