diff --git a/imagekit/models.py b/imagekit/models.py
index 28efc75..b247b21 100755
--- a/imagekit/models.py
+++ b/imagekit/models.py
@@ -77,6 +77,13 @@ class ImageSpec(_ImageSpecMixin):
 
     def contribute_to_class(self, cls, name):
         setattr(cls, name, _ImageSpecDescriptor(self, name))
+        try:
+            ik = getattr(cls, '_ik')
+        except AttributeError:
+            ik = type('ImageKitMeta', (object,), {'spec_file_names': []})
+            setattr(cls, '_ik', ik)
+        ik.spec_file_names.append(name)
+
         # Connect to the signals only once for this class.
         uid = '%s.%s' % (cls.__module__, cls.__name__)
         post_save.connect(_post_save_handler,
diff --git a/imagekit/utils.py b/imagekit/utils.py
index 29d9da2..3c9c7c3 100644
--- a/imagekit/utils.py
+++ b/imagekit/utils.py
@@ -13,16 +13,12 @@ def img_to_fobj(img, format, **kwargs):
 
 
 def get_spec_files(instance):
-    from imagekit.models import ImageSpecFile
-    spec_files = []
-    for key in dir(instance):
-        try:
-            value = getattr(instance, key)
-        except AttributeError:
-            continue
-        if isinstance(value, ImageSpecFile):
-            spec_files.append(value)
-    return spec_files
+    try:
+        ik = getattr(instance, '_ik')
+    except AttributeError:
+        return []
+    else:
+        return [getattr(instance, n) for n in ik.spec_file_names]
 
 
 def open_image(target):