diff --git a/git/util.py b/git/util.py
index 2d4cc7c23..c7450b53d 100644
--- a/git/util.py
+++ b/git/util.py
@@ -401,7 +401,7 @@ def assure_directory_exists(path: PathLike, is_file: bool = False) -> bool:
         ``True`` if the directory was created, ``False`` if it already existed.
     """
     if is_file:
-        path = osp.dirname(path)
+        path = osp.dirname(path) or osp.curdir
     # END handle file
     if not osp.isdir(path):
         os.makedirs(path, exist_ok=True)
diff --git a/test/test_assure_directory.py b/test/test_assure_directory.py
new file mode 100644
index 000000000..04de1993f
--- /dev/null
+++ b/test/test_assure_directory.py
@@ -0,0 +1,42 @@
+from pathlib import Path
+
+import pytest
+
+from git.util import assure_directory_exists
+from test.lib.fixtures import writable_fixture
+
+
+@pytest.fixture
+def directory_fixture(monkeypatch):
+    with writable_fixture("assure-directory.sh") as temporary:
+        directory = temporary.path().resolve()
+        with monkeypatch.context() as context:
+            context.chdir(directory)
+            yield directory
+
+
+@pytest.mark.parametrize("path_type", [str, Path])
+def test_file_in_current_directory_already_has_parent(directory_fixture, path_type):
+    assert assure_directory_exists(path_type("notes.txt"), is_file=True) is False
+    assert not (directory_fixture / "notes.txt").exists()
+
+
+@pytest.mark.parametrize("path_type", [str, Path])
+def test_nested_file_creates_only_missing_parent_directories(directory_fixture, path_type):
+    filename = path_type("new/nested/notes.txt")
+    assert assure_directory_exists(filename, is_file=True) is True
+    assert (directory_fixture / "new/nested").is_dir()
+    assert not (directory_fixture / "new/nested/notes.txt").exists()
+    assert assure_directory_exists(filename, is_file=True) is False
+
+
+@pytest.mark.parametrize("path_type", [str, Path])
+def test_existing_directory_is_unchanged(directory_fixture, path_type):
+    assert assure_directory_exists(path_type("existing")) is False
+
+
+@pytest.mark.parametrize("path_type", [str, Path])
+def test_file_cannot_be_used_as_parent_directory(directory_fixture, path_type):
+    with pytest.raises(FileExistsError):
+        assure_directory_exists(path_type("blocked/notes.txt"), is_file=True)
+    assert (directory_fixture / "blocked").read_text() == "occupied\n"
diff --git a/tests/fixtures/assure-directory.sh b/tests/fixtures/assure-directory.sh
new file mode 100644
index 000000000..438236991
--- /dev/null
+++ b/tests/fixtures/assure-directory.sh
@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+set -eu
+mkdir existing
+printf 'occupied\n' > blocked