diff --git a/imagekit/specs/__init__.py b/imagekit/specs/__init__.py
index de1db8d..79ff107 100644
--- a/imagekit/specs/__init__.py
+++ b/imagekit/specs/__init__.py
@@ -104,7 +104,7 @@ class ImageSpec(BaseImageSpec):
 
     def get_hash(self):
         return md5(pickle.dumps([
-            self.source,
+            self.source.name,
             self.kwargs,
             self.processors,
             self.format,