diff --git a/src/config.cc b/src/config.cc
index 0d008cb..faecd5d 100644
--- a/src/config.cc
+++ b/src/config.cc
@@ -161,4 +161,5 @@ void Config::usage() {
 	printf("Mandatory options:\n");
 	printf("-g, -group <host:port>      Add an host to the group\n");
 	printf("-p, -port <port>            Use this port on localhost\n");
+	printf("-i, -index <int>            The index of current host in the group\n");
 }