diff --git a/builtin/commit-tree.c b/builtin/commit-tree.c
index 05353c3..164b655 100644
--- a/builtin/commit-tree.c
+++ b/builtin/commit-tree.c
@@ -8,8 +8,9 @@
 #include "tree.h"
 #include "builtin.h"
 #include "utf8.h"
+#include "gpg-interface.h"
 
-static const char commit_tree_usage[] = "git commit-tree [(-p <sha1>)...] [-m <message>] [-F <file>] <sha1> <changelog";
+static const char commit_tree_usage[] = "git commit-tree [(-p <sha1>)...] [-S<signer>] [-m <message>] [-F <file>] <sha1> <changelog";
 
 static void new_parent(struct commit *parent, struct commit_list **parents_p)
 {
@@ -25,6 +26,14 @@
 	commit_list_insert(parent, parents_p);
 }
 
+static int commit_tree_config(const char *var, const char *value, void *cb)
+{
+	int status = git_gpg_config(var, value, NULL);
+	if (status)
+		return status;
+	return git_default_config(var, value, cb);
+}
+
 int cmd_commit_tree(int argc, const char **argv, const char *prefix)
 {
 	int i, got_tree = 0;
@@ -32,12 +41,16 @@
 	unsigned char tree_sha1[20];
 	unsigned char commit_sha1[20];
 	struct strbuf buffer = STRBUF_INIT;
+	const char *sign_commit = NULL;
 
-	git_config(git_default_config, NULL);
+	git_config(commit_tree_config, NULL);
 
 	if (argc < 2 || !strcmp(argv[1], "-h"))
 		usage(commit_tree_usage);
 
+	if (get_sha1(argv[1], tree_sha1))
+		die("Not a valid object name %s", argv[1]);
+
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
 		if (!strcmp(arg, "-p")) {
@@ -51,6 +64,11 @@
 			continue;
 		}
 
+		if (!memcmp(arg, "-S", 2)) {
+			sign_commit = arg + 2;
+			continue;
+		}
+
 		if (!strcmp(arg, "-m")) {
 			if (argc <= ++i)
 				usage(commit_tree_usage);
@@ -98,7 +116,8 @@
 			die_errno("git commit-tree: failed to read");
 	}
 
-	if (commit_tree(&buffer, tree_sha1, parents, commit_sha1, NULL)) {
+	if (commit_tree(&buffer, tree_sha1, parents, commit_sha1,
+			NULL, sign_commit)) {
 		strbuf_release(&buffer);
 		return 1;
 	}