diff --git a/googleapiclient/_auth.py b/googleapiclient/_auth.py
index 05a1d38..92f2796 100644
--- a/googleapiclient/_auth.py
+++ b/googleapiclient/_auth.py
@@ -126,7 +126,8 @@
         return None
     elif hasattr(http.request, 'credentials'):
         return http.request.credentials
-    elif hasattr(http, 'credentials'):
+    elif (hasattr(http, 'credentials')
+          and not isinstance(http.credentials, httplib2.Credentials)):
         return http.credentials
     else:
         return None