diff --git a/jaas-jwt-samples/python/jass-jwt.py b/jaas-jwt-samples/python/jass-jwt.py
index 35ac27e..386db87 100644
--- a/jaas-jwt-samples/python/jass-jwt.py
+++ b/jaas-jwt-samples/python/jass-jwt.py
@@ -128,7 +128,7 @@ def withNbfTime(self, nbfTime):
 
         :param nbfTime Unix time in seconds since epochs.
         """
-        self.payloadClaims['nbfTime'] = nbfTime
+        self.payloadClaims['nbf'] = nbfTime
         return self
 
     def withRoomName(self, roomName):