diff --git a/sbin/ipfw/ipfw2.c b/sbin/ipfw/ipfw2.c
--- a/sbin/ipfw/ipfw2.c
+++ b/sbin/ipfw/ipfw2.c
@@ -4961,6 +4961,7 @@
 			break;
 
 		case TOK_EXT6HDR:
+			NEED1("missing extension header");
 			fill_ext6hdr( cmd, *av );
 			av++;
 			break;