ext/RMagick/rmimage.c in rmagick-2.13.2 vs ext/RMagick/rmimage.c in rmagick-2.13.3.rc1

@@ -9817,10 +9817,10 @@
 #if defined(HAVE_GETAUTHENTICINDEXQUEUE)
             IndexPacket *indexes = GetAuthenticIndexQueue(image);
 #else
             IndexPacket *indexes = GetIndexes(image);
 #endif
-            old_color = image->colormap[*indexes];
+            old_color = image->colormap[(unsigned long)*indexes];
         }
         if (!image->matte)
         {
             old_color.opacity = OpaqueOpacity;
         }