diff --git a/pyVoIP/SIP/client.py b/pyVoIP/SIP/client.py
index 78b10c8..04943a2 100644
--- a/pyVoIP/SIP/client.py
+++ b/pyVoIP/SIP/client.py
@@ -429,7 +429,7 @@ def gen_digest(
         else:
             hash_func = self._hash_md5
         # Get new method values
-        qop = request.authentication.get("qop", None).pop(0)
+        qop = request.authentication.get("qop", [None]).pop(0)
         opaque = request.authentication.get("opaque", None)
         userhash = request.authentication.get("userhash", False)