diff -u b/modules/system/image.gd.inc b/modules/system/image.gd.inc
--- b/modules/system/image.gd.inc
+++ b/modules/system/image.gd.inc
@@ -132,7 +132,7 @@
     $background = imagecolortransparent($image->resource);
 
     // If no transparent colors, use transparent white.
-    if ($background == 0) {
+    if ($background === -1) {
       $background = array('red' => 255, 'green' => 255, 'blue' => 255, 'alpha' => 127);
     }
   }