diff --git a/oauth2client/contrib/flask_util.py b/oauth2client/contrib/flask_util.py
index c8cd2e823..517bcdf86 100644
--- a/oauth2client/contrib/flask_util.py
+++ b/oauth2client/contrib/flask_util.py
@@ -199,7 +199,7 @@ def requires_calendar():
 def _get_flow_for_token(csrf_token):
     """Retrieves the flow instance associated with a given CSRF token from
     the Flask session."""
-    flow_pickle = session.get(
+    flow_pickle = session.pop(
         _FLOW_KEY.format(csrf_token), None)
 
     if flow_pickle is None: