--- libpng3-1.2.1.orig/pngerror.c
+++ libpng3-1.2.1/pngerror.c
@@ -134,10 +134,14 @@
       buffer[iout] = 0;
    else
    {
+      int len = strlen(message);
+
+      if (len > 63)
+         len = 63;
       buffer[iout++] = ':';
       buffer[iout++] = ' ';
-      png_memcpy(buffer+iout, message, 64);
-      buffer[iout+63] = 0;
+      png_memcpy(buffer+iout, message, len);
+      buffer[iout+len] = 0;
    }
 }