diff --git a/src/userfunc.c b/src/userfunc.c
index 223535f..7341878 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3262,7 +3262,7 @@
     typval_T	rettv;
     varnumber_T	retval;
 
-    if (call_callback(callback, 0, &rettv, argcount, argvars) == FAIL)
+    if (call_callback(callback, -1, &rettv, argcount, argvars) == FAIL)
 	return -2;
 
     retval = tv_get_number_chk(&rettv, NULL);