diff --git a/gcloud/pubsub/client.py b/gcloud/pubsub/client.py
index 95164287499b..24c51f4697c2 100644
--- a/gcloud/pubsub/client.py
+++ b/gcloud/pubsub/client.py
@@ -39,7 +39,7 @@
     _HAVE_GAX = True
 
 
-_USE_GAX = _HAVE_GAX and os.environ.get('GCLOUD_DISABLE_GAX') is None
+_USE_GAX = _HAVE_GAX and (os.environ.get('GCLOUD_ENABLE_GAX') is not None)
 
 
 class Client(JSONClient):