diff --git a/Documentation/git-commit-tree.txt b/Documentation/git-commit-tree.txt
index 86ef56e7c..cafdc9642 100644
--- a/Documentation/git-commit-tree.txt
+++ b/Documentation/git-commit-tree.txt
@@ -10,7 +10,9 @@ SYNOPSIS
 --------
 [verse]
 'git commit-tree' <tree> [(-p <parent>)...] < changelog
-'git commit-tree' [(-p <parent>)...] [(-m <message>)...] [(-F <file>)...] <tree>
+'git commit-tree' [(-p <parent>)...] [-S[<keyid>]] [(-m <message>)...]
+		  [(-F <file>)...] <tree>
+
 
 DESCRIPTION
 -----------
@@ -52,6 +54,9 @@ OPTIONS
 	Read the commit log message from the given file. Use `-` to read
 	from the standard input.
 
+-S[<keyid>]::
+	GPG-sign commit.
+
 
 Commit Information
 ------------------
diff --git a/builtin/commit-tree.c b/builtin/commit-tree.c
index eac901a0e..f641ff2a8 100644
--- a/builtin/commit-tree.c
+++ b/builtin/commit-tree.c
@@ -10,7 +10,7 @@
 #include "utf8.h"
 #include "gpg-interface.h"
 
-static const char commit_tree_usage[] = "git commit-tree [(-p <sha1>)...] [-S<signer>] [-m <message>] [-F <file>] <sha1> <changelog";
+static const char commit_tree_usage[] = "git commit-tree [(-p <sha1>)...] [-S[<keyid>]] [-m <message>] [-F <file>] <sha1> <changelog";
 
 static void new_parent(struct commit *parent, struct commit_list **parents_p)
 {