diff --git a/cmd/kubeadm/app/cmd/init.go b/cmd/kubeadm/app/cmd/init.go
index 666de7e2f50..041cc673233 100644
--- a/cmd/kubeadm/app/cmd/init.go
+++ b/cmd/kubeadm/app/cmd/init.go
@@ -187,7 +187,7 @@ func AddInitConfigFlags(flagSet *flag.FlagSet, cfg *kubeadmapiext.MasterConfigur
 	)
 	flagSet.StringVar(
 		&cfg.Token, "token", cfg.Token,
-		"The token to use for establishing bidirectional trust between nodes and masters.",
+		"The token to use for establishing bidirectional trust between nodes and masters. The format is [a-z0-9]{6}\\.[a-z0-9]{16} - e.g. abcdef.0123456789abcdef",
 	)
 	flagSet.DurationVar(
 		&cfg.TokenTTL.Duration, "token-ttl", cfg.TokenTTL.Duration,