diff --git a/src/vty/command.c b/src/vty/command.c
index 16dd07f..278ceb5 100644
--- a/src/vty/command.c
+++ b/src/vty/command.c
@@ -1325,6 +1325,9 @@
 	} else {
 		unsigned long min, max, val;
 
+		if (str[0] == '-')
+			return 0;
+
 		val = strtoul(str, &endptr, 10);
 		if (*endptr != '\0')
 			return 0;