Index: libmapi/IMAPISupport.c
===================================================================
--- libmapi/IMAPISupport.c	(revision 1271)
+++ libmapi/IMAPISupport.c	(working copy)
@@ -93,6 +93,7 @@
 
 	session = mapi_object_get_session(obj);
 	OPENCHANGE_RETVAL_IF(!session, MAPI_E_INVALID_PARAMETER, NULL);
+	OPENCHANGE_RETVAL_IF(!session->notify_ctx, MAPI_E_INVALID_PARAMETER, NULL);
 
 	mem_ctx = talloc_named(NULL, 0, "Subscribe");