diff --git a/src/typval.c b/src/typval.c
index af96b31..62958f6 100644
--- a/src/typval.c
+++ b/src/typval.c
@@ -623,6 +623,16 @@
 	    || check_for_dict_arg(args, idx) != FAIL) ? OK : FAIL;
 }
 
+/*
+ * Check for an optional non-NULL dict argument at 'idx'
+ */
+    int
+check_for_opt_nonnull_dict_arg(typval_T *args, int idx)
+{
+    return (args[idx].v_type == VAR_UNKNOWN
+	    || check_for_nonnull_dict_arg(args, idx) != FAIL) ? OK : FAIL;
+}
+
 #if defined(FEAT_JOB_CHANNEL) || defined(PROTO)
 /*
  * Give an error and return FAIL unless "args[idx]" is a channel or a job.