diff --git a/ox/api.py b/ox/api.py
index 3b57ae2..9717ff2 100644
--- a/ox/api.py
+++ b/ox/api.py
@@ -52,6 +52,8 @@ class API(object):
 
     def _add_action(self, action):
         def method(self, *args, **kw):
+            if args and kw:
+                raise ValueError('pass either a dictionary or kwargs, not both')
             if not kw:
                 if args:
                     kw = args[0]