diff --git a/ANNOUNCE b/ANNOUNCE
index d7c6be33..1e19681d 100644
--- a/ANNOUNCE
+++ b/ANNOUNCE
@@ -1,5 +1,5 @@
 
-Libpng 1.2.55beta01 - November 13, 2015
+Libpng 1.2.55beta01 - November 14, 2015
 
 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.
@@ -43,7 +43,9 @@ Other information:
 
 Changes since the last public release (1.2.54):
 
-version 1.2.55beta01 [November 13, 2015]
+version 1.2.55beta01 [November 14, 2015]
+  Avoid potential pointer overflow in png_handle_iTXt(), png_handle_zTXt(),
+    png_handle_sPLT(), and png_handle_pCAL() (Bug report by John Regehr).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/CHANGES b/CHANGES
index b82f0ddd..c98b33da 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2895,6 +2895,8 @@ version 1.2.54 [November 12, 2015]
   Cleaned up coding style in png_handle_PLTE().
    
 version 1.2.55beta01 [%RDATE%]
+  Avoid potential pointer overflow in png_handle_iTXt(), png_handle_zTXt(),
+    png_handle_sPLT(), and png_handle_pCAL() (Bug report by John Regehr).
 
 Send comments/corrections/commendations to png-mng-implement at lists.sf.net
 (subscription required; visit
diff --git a/pngrutil.c b/pngrutil.c
index 50cc9719..320ebb9c 100644
--- a/pngrutil.c
+++ b/pngrutil.c
@@ -1114,7 +1114,7 @@ png_handle_iCCP(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
    /* There should be at least one zero (the compression type byte)
     * following the separator, and we should be on it
     */
-   if ( profile >= png_ptr->chunkdata + slength - 1)
+   if (slength < 1 ||  profile >= png_ptr->chunkdata + slength - 1)
    {
       png_free(png_ptr, png_ptr->chunkdata);
       png_ptr->chunkdata = NULL;
@@ -1242,7 +1242,7 @@ png_handle_sPLT(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
    ++entry_start;
 
    /* A sample depth should follow the separator, and we should be on it  */
-   if (entry_start > (png_bytep)png_ptr->chunkdata + slength - 2)
+   if (slength < 2 || entry_start > (png_bytep)png_ptr->chunkdata + slength - 2)
    {
       png_free(png_ptr, png_ptr->chunkdata);
       png_ptr->chunkdata = NULL;
@@ -1716,7 +1716,7 @@ png_handle_pCAL(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
 
    /* We need to have at least 12 bytes after the purpose string
       in order to get the parameter information. */
-   if (endptr <= buf + 12)
+   if (slength < 12 || endptr <= buf + 12)
    {
       png_warning(png_ptr, "Invalid pCAL data");
       png_free(png_ptr, png_ptr->chunkdata);
@@ -2172,7 +2172,7 @@ png_handle_zTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
       /* Empty loop */ ;
 
    /* zTXt must have some text after the chunkdataword */
-   if (text >= png_ptr->chunkdata + slength - 2)
+   if (slength < 2 || text >= png_ptr->chunkdata + slength - 2)
    {
       png_warning(png_ptr, "Truncated zTXt chunk");
       png_free(png_ptr, png_ptr->chunkdata);
@@ -2298,7 +2298,7 @@ png_handle_iTXt(png_structp png_ptr, png_infop info_ptr, png_uint_32 length)
     * keyword
     */
 
-   if (lang >= png_ptr->chunkdata + slength - 3)
+   if (slength < 3 || lang >= png_ptr->chunkdata + slength - 3)
    {
       png_warning(png_ptr, "Truncated iTXt chunk");
       png_free(png_ptr, png_ptr->chunkdata);