diff --git a/git-codereview/mail.go b/git-codereview/mail.go
index c96caff..55e2c28 100644
--- a/git-codereview/mail.go
+++ b/git-codereview/mail.go
@@ -43,7 +43,7 @@
 	if len(flags.Args()) == 1 {
 		c = b.CommitByRev("mail", flags.Arg(0))
 	} else {
-		c = b.DefaultCommit("mail", "must specify commit on command line")
+		c = b.DefaultCommit("mail", "must specify commit on command line or use mail HEAD for everything")
 	}
 
 	if *diff {