diff --git a/pyghmi/ipmi/private/session.py b/pyghmi/ipmi/private/session.py
index 184be97f..e3df0d13 100644
--- a/pyghmi/ipmi/private/session.py
+++ b/pyghmi/ipmi/private/session.py
@@ -958,6 +958,8 @@ class Session(object):
         return regid
 
     def unregister_keepalive(self, regid):
+        if self._customkeepalives is None:
+            return
         try:
             del self._customkeepalives[regid]
         except KeyError: