diff --git a/sys/netgraph/ng_parse.c b/sys/netgraph/ng_parse.c
--- a/sys/netgraph/ng_parse.c
+++ b/sys/netgraph/ng_parse.c
@@ -1207,6 +1207,8 @@
 	int align, len, blen, error = 0;
 
 	/* Initialize */
+	if (num < 0)
+		return (EINVAL);
 	foff = malloc(num * sizeof(*foff), M_NETGRAPH_PARSE, M_NOWAIT | M_ZERO);
 	if (foff == NULL) {
 		error = ENOMEM;