diff --git a/foolbox/models/tensorflow.py b/foolbox/models/tensorflow.py
index 730b413f..ab0c0db6 100644
--- a/foolbox/models/tensorflow.py
+++ b/foolbox/models/tensorflow.py
@@ -50,6 +50,8 @@ def __init__(
             self._created_session = True
         else:
             self._created_session = False
+            assert session.graph == images.graph, \
+                'The default session uses the wrong graph'
 
         with session.graph.as_default():
             self._session = session