1 files changed, 4 insertions, 0 deletions
diff --git a/main.go b/main.go
index 1ca9563..6d27c21 100644
--- a/main.go
+++ b/main.go
@@ -576,6 +576,10 @@ func printLossyPathsJSON(sent, rcvd map[int] /* src port */ []int, hops map[int]
 
 func main() {
 	flag.Parse()
+	if flag.Arg(0) == "" {
+		fmt.Fprintf(os.Stderr, "Must specify a target\n")
+		return
+	}
 	target := flag.Arg(0)
 
 	var probes []chan interface{}