diff --git a/Documentation/git-fast-import.txt b/Documentation/git-fast-import.txt
index 966ba4f21..90a46665c 100644
--- a/Documentation/git-fast-import.txt
+++ b/Documentation/git-fast-import.txt
@@ -524,6 +524,9 @@ start with double quote (`"`).
 If an `LF` or double quote must be encoded into `<path>` shell-style
 quoting should be used, e.g. `"path/with\n and \" in it"`.
 
+Additionally, in `040000` mode, `<path>` may also be an empty string
+(`""`) to specify the root of the tree.
+
 The value of `<path>` must be in canonical form. That is it must not:
 
 * contain an empty directory component (e.g. `foo//bar` is invalid),
diff --git a/fast-import.c b/fast-import.c
index 2317b0fe7..8f68a8923 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -1454,6 +1454,15 @@ static int tree_content_set(
 		n = slash1 - p;
 	else
 		n = strlen(p);
+	if (!slash1 && !n) {
+		if (!S_ISDIR(mode))
+			die("Root cannot be a non-directory");
+		hashcpy(root->versions[1].sha1, sha1);
+		if (root->tree)
+			release_tree_content_recursive(root->tree);
+		root->tree = subtree;
+		return 1;
+	}
 	if (!n)
 		die("Empty path component found in input");
 	if (!slash1 && !S_ISDIR(mode) && subtree)
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 7c059204e..3c0cf0509 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -874,6 +874,27 @@ test_expect_success \
 	 git diff-tree -C --find-copies-harder -r N4^ N4 >actual &&
 	 compare_diff_raw expect actual'
 
+test_expect_success \
+	'N: copy root directory by tree hash' \
+	'cat >expect <<-\EOF &&
+	:100755 000000 f1fb5da718392694d0076d677d6d0e364c79b0bc 0000000000000000000000000000000000000000 D	file3/newf
+	:100644 000000 7123f7f44e39be127c5eb701e5968176ee9d78b1 0000000000000000000000000000000000000000 D	file3/oldf
+	EOF
+	 root=$(git rev-parse refs/heads/branch^0^{tree}) &&
+	 cat >input <<-INPUT_END &&
+	commit refs/heads/N6
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	copy root directory by tree hash
+	COMMIT
+
+	from refs/heads/branch^0
+	M 040000 $root ""
+	INPUT_END
+	 git fast-import <input &&
+	 git diff-tree -C --find-copies-harder -r N4 N6 >actual &&
+	 compare_diff_raw expect actual'
+
 test_expect_success \
 	'N: modify copied tree' \
 	'cat >expect <<-\EOF &&