diff --git a/unifier/models.py b/unifier/models.py
index f6496d8402f045b2f00d27f63065a73e892041cb..2fd744c3d705d61294d0ad4f65947441767d533c 100644
--- a/unifier/models.py
+++ b/unifier/models.py
@@ -53,7 +53,7 @@ class UnifiedFrame(models.Model):
             new_unified_frame_arguments = UnifiedFrameArgument.objects.filter(unified_frame=new_frame).all()
             unified_frame_arguments = UnifiedFrameArgument.objects.filter(unified_frame=self).all()
             if len(new_unified_frame_arguments) < len(unified_frame_arguments):
-                raise Exception('Target frame has to little arguments, required: ' + len(unified_frame_arguments)+', but found: '+len(new_unified_frame_arguments))
+                raise Exception('Target frame has to little arguments, required: ' + str(len(unified_frame_arguments))+', but found: '+str(len(new_unified_frame_arguments)))
 
         for slowal_frame in slowal_frames:
             mapping = UnifiedFrame2SlowalFrameMapping.objects.get(unified_frame=self, slowal_frame=slowal_frame)