diff --git a/Makefile b/Makefile
index a041b69561..969adc7e20 100644
--- a/Makefile
+++ b/Makefile
@@ -391,7 +391,6 @@ PROGRAMS += git-hash-object$X
 PROGRAMS += git-imap-send$X
 PROGRAMS += git-index-pack$X
 PROGRAMS += git-merge-index$X
-PROGRAMS += git-merge-tree$X
 PROGRAMS += git-mktag$X
 PROGRAMS += git-pack-redundant$X
 PROGRAMS += git-patch-id$X
@@ -672,6 +671,7 @@ BUILTIN_OBJS += builtin-merge-base.o
 BUILTIN_OBJS += builtin-merge-file.o
 BUILTIN_OBJS += builtin-merge-ours.o
 BUILTIN_OBJS += builtin-merge-recursive.o
+BUILTIN_OBJS += builtin-merge-tree.o
 BUILTIN_OBJS += builtin-mktree.o
 BUILTIN_OBJS += builtin-mv.o
 BUILTIN_OBJS += builtin-name-rev.o
diff --git a/merge-tree.c b/builtin-merge-tree.c
similarity index 99%
rename from merge-tree.c
rename to builtin-merge-tree.c
index 37b94d976c..8e16c3edad 100644
--- a/merge-tree.c
+++ b/builtin-merge-tree.c
@@ -337,7 +337,7 @@ static void *get_tree_descriptor(struct tree_desc *desc, const char *rev)
 	return buf;
 }
 
-int main(int argc, char **argv)
+int cmd_merge_tree(int argc, const char **argv, const char *prefix)
 {
 	struct tree_desc t[3];
 	void *buf1, *buf2, *buf3;
@@ -347,8 +347,6 @@ int main(int argc, char **argv)
 
 	git_extract_argv0_path(argv[0]);
 
-	setup_git_directory();
-
 	buf1 = get_tree_descriptor(t+0, argv[1]);
 	buf2 = get_tree_descriptor(t+1, argv[2]);
 	buf3 = get_tree_descriptor(t+2, argv[3]);
diff --git a/builtin.h b/builtin.h
index c3f83c093f..0936ad2667 100644
--- a/builtin.h
+++ b/builtin.h
@@ -70,6 +70,7 @@ extern int cmd_merge_base(int argc, const char **argv, const char *prefix);
 extern int cmd_merge_ours(int argc, const char **argv, const char *prefix);
 extern int cmd_merge_file(int argc, const char **argv, const char *prefix);
 extern int cmd_merge_recursive(int argc, const char **argv, const char *prefix);
+extern int cmd_merge_tree(int argc, const char **argv, const char *prefix);
 extern int cmd_mktree(int argc, const char **argv, const char *prefix);
 extern int cmd_mv(int argc, const char **argv, const char *prefix);
 extern int cmd_name_rev(int argc, const char **argv, const char *prefix);
diff --git a/git.c b/git.c
index 194471f5b1..15b13bd1b9 100644
--- a/git.c
+++ b/git.c
@@ -335,6 +335,7 @@ static void handle_internal_command(int argc, const char **argv)
 		{ "merge-recursive-ours", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE },
 		{ "merge-recursive-theirs", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE },
 		{ "merge-subtree", cmd_merge_recursive, RUN_SETUP | NEED_WORK_TREE },
+		{ "merge-tree", cmd_merge_tree, RUN_SETUP },
 		{ "mktree", cmd_mktree, RUN_SETUP },
 		{ "mv", cmd_mv, RUN_SETUP | NEED_WORK_TREE },
 		{ "name-rev", cmd_name_rev, RUN_SETUP },