diff --git a/fast-import.c b/fast-import.c
index aaf47c574..cb947c10d 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -1437,6 +1437,20 @@ static void store_tree(struct tree_entry *root)
 	t->entry_count -= del;
 }
 
+static void tree_content_replace(
+	struct tree_entry *root,
+	const unsigned char *sha1,
+	const uint16_t mode,
+	struct tree_content *newtree)
+{
+	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 = newtree;
+}
+
 static int tree_content_set(
 	struct tree_entry *root,
 	const char *p,
@@ -1454,15 +1468,6 @@ 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)
@@ -2230,6 +2235,10 @@ static void file_change_m(struct branch *b)
 				command_buf.buf);
 	}
 
+	if (!*p) {
+		tree_content_replace(&b->branch_tree, sha1, mode, NULL);
+		return;
+	}
 	tree_content_set(&b->branch_tree, p, sha1, mode, NULL);
 }
 
@@ -2288,6 +2297,13 @@ static void file_change_cr(struct branch *b, int rename)
 		tree_content_get(&b->branch_tree, s, &leaf);
 	if (!leaf.versions[1].mode)
 		die("Path %s not in branch", s);
+	if (!*d) {	/* C "path/to/subdir" "" */
+		tree_content_replace(&b->branch_tree,
+			leaf.versions[1].sha1,
+			leaf.versions[1].mode,
+			leaf.tree);
+		return;
+	}
 	tree_content_set(&b->branch_tree, d,
 		leaf.versions[1].sha1,
 		leaf.versions[1].mode,
diff --git a/t/t9300-fast-import.sh b/t/t9300-fast-import.sh
index 1df11adc9..ce094577e 100755
--- a/t/t9300-fast-import.sh
+++ b/t/t9300-fast-import.sh
@@ -928,6 +928,20 @@ test_expect_success \
 	 git diff-tree -C --find-copies-harder -r N5^^ N5 >actual &&
 	 compare_diff_raw expect actual'
 
+test_expect_success \
+	'N: reject foo/ syntax' \
+	'subdir=$(git rev-parse refs/heads/branch^0:file2) &&
+	 test_must_fail git fast-import <<-INPUT_END
+	commit refs/heads/N5B
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	copy with invalid syntax
+	COMMIT
+
+	from refs/heads/branch^0
+	M 040000 $subdir file3/
+	INPUT_END'
+
 test_expect_success \
 	'N: copy to root by id and modify' \
 	'echo "hello, world" >expect.foo &&
@@ -965,6 +979,22 @@ test_expect_success \
 	 test_cmp expect.foo actual.foo &&
 	 test_cmp expect.bar actual.bar'
 
+test_expect_success \
+	'N: extract subtree' \
+	'branch=$(git rev-parse --verify refs/heads/branch^{tree}) &&
+	 cat >input <<-INPUT_END &&
+	commit refs/heads/N9
+	committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
+	data <<COMMIT
+	extract subtree branch:newdir
+	COMMIT
+
+	M 040000 $branch ""
+	R "newdir" ""
+	INPUT_END
+	 git fast-import <input &&
+	 git diff --exit-code branch:newdir N9'
+
 ###
 ### series O
 ###