diff --git a/ipfw/ipfw2.c b/ipfw/ipfw2.c
index b8ef6ee..e66a979 100644
--- a/ipfw/ipfw2.c
+++ b/ipfw/ipfw2.c
@@ -2935,6 +2935,8 @@ fill_ip(ipfw_insn_ip *cmd, char *av, int cblen, struct tidx *tstate)
 			    i = a;
 			else if (*s == '}')
 			    break;
+			else if (*s == '\0')
+				break;
 			av = s+1;
 		}
 		return;