diff --git a/imagekit/specs/__init__.py b/imagekit/specs/__init__.py
index eb98975..e29cdb6 100644
--- a/imagekit/specs/__init__.py
+++ b/imagekit/specs/__init__.py
@@ -23,7 +23,7 @@ class SpecRegistry(object):
         self._specs = {}
         self._sources = {}
         for signal in self.signals.keys():
-            signal.connect(lambda *a, **k: self.source_receiver(signal, *a, **k))
+            signal.connect(self.source_receiver)
 
     def register(self, id, spec):
         if id in self._specs:
@@ -51,11 +51,12 @@ class SpecRegistry(object):
             self._sources[source] = set()
         self._sources[source].add(spec_id)
 
-    def source_receiver(self, signal, source, source_file):
+    def source_receiver(self, sender, source_file, signal, **kwargs):
+        source = sender
         if source not in self._sources:
             return
 
-        callback_name = self._signals[signal]
+        callback_name = self.signals[signal]
         for spec in (self.get_spec(id) for id in self._sources[source]):
             spec.image_cache_strategy.invoke_callback(callback_name, source_file)
 
diff --git a/imagekit/specs/sources.py b/imagekit/specs/sources.py
index 807ee2a..183180d 100644
--- a/imagekit/specs/sources.py
+++ b/imagekit/specs/sources.py
@@ -65,20 +65,20 @@ class ModelSignalRouter(object):
             new_hashes = self.update_source_hashes(instance)
             for attname, file in self.get_field_dict(instance).items():
                 if created:
-                    self.dispatch_signal(source_created, sender, file)
+                    self.dispatch_signal(source_created, file, sender)
                 elif old_hashes[attname] != new_hashes[attname]:
-                    self.dispatch_signal(source_changed, sender, file)
+                    self.dispatch_signal(source_changed, file, sender)
 
     @ik_model_receiver
     def post_delete_receiver(self, sender, instance=None, **kwargs):
         for attname, file in self.get_field_dict(instance):
-            self.dispatch_signal(source_deleted, sender, file)
+            self.dispatch_signal(source_deleted, file, sender)
 
     @ik_model_receiver
     def post_init_receiver(self, sender, instance=None, **kwargs):
         self.update_source_hashes(instance)
 
-    def dispatch_signal(self, signal, model_class, file):
+    def dispatch_signal(self, signal, file, model_class):
         """
         Dispatch the signal for each of the matching sources. Note that more
         than one source can have the same model and image_field; it's important
@@ -86,7 +86,8 @@ class ModelSignalRouter(object):
 
         """
         for source in self._sources:
-            if source.model_class is model_class and source.image_field == file.attname:
+            # TODO: Is it okay to require a field attribute on our file?
+            if source.model_class is model_class and source.image_field == file.field.attname:
                 signal.send(sender=source, source_file=file)