diff --git a/cmd/minimal-download/main.go b/cmd/minimal-download/main.go
index 605fd93..a8a1a00 100644
--- a/cmd/minimal-download/main.go
+++ b/cmd/minimal-download/main.go
@@ -325,6 +325,10 @@ outer:
 func main() {
 	flag.Parse()
 
+	if *flagStreams < 1 || *flagStreams > 4 {
+		log.Fatal("Invalid configuration: the number of streams must be between 1 and 4.")
+	}
+
 	ctx, cancel := context.WithTimeout(context.Background(), *flagMaxDuration)
 	defer cancel()
 
diff --git a/cmd/msak-client/client.go b/cmd/msak-client/client.go
index 2f65ebb..ebc0557 100644
--- a/cmd/msak-client/client.go
+++ b/cmd/msak-client/client.go
@@ -38,6 +38,10 @@ func main() {
 		log.Fatal("Invalid configuration: please check streams, delay and duration and make sure they make sense.")
 	}
 
+	if *flagStreams < 1 || *flagStreams > 4 {
+		log.Fatal("Invalid configuration: the number of streams must be between 1 and 4.")
+	}
+
 	config := client.Config{
 		Server:            *flagServer,
 		Scheme:            *flagScheme,