diff --git a/src/anthropic/lib/_files.py b/src/anthropic/lib/_files.py
index ad7b7e57a..c022829d5 100644
--- a/src/anthropic/lib/_files.py
+++ b/src/anthropic/lib/_files.py
@@ -9,7 +9,9 @@
 
 
 def files_from_dir(directory: str | os.PathLike[str]) -> list[FileTypes]:
-    path = Path(directory)
+    # the names carry the directory itself, so where it sits has to be known:
+    # `.` has no parent to take the name from, and `..` would put one in a name
+    path = Path(os.path.abspath(directory))
 
     files: list[FileTypes] = []
     _collect_files(path, path.parent, files)
@@ -26,7 +28,7 @@ def _collect_files(directory: Path, relative_to: Path, files: list[FileTypes]) -
 
 
 async def async_files_from_dir(directory: str | os.PathLike[str]) -> list[FileTypes]:
-    path = anyio.Path(directory)
+    path = anyio.Path(os.path.abspath(directory))
 
     files: list[FileTypes] = []
     await _async_collect_files(path, path.parent, files)
diff --git a/tests/lib/test_files.py b/tests/lib/test_files.py
new file mode 100644
index 000000000..13f49a0a4
--- /dev/null
+++ b/tests/lib/test_files.py
@@ -0,0 +1,53 @@
+from __future__ import annotations
+
+import os
+from pathlib import Path
+
+import pytest
+
+from anthropic.lib import files_from_dir, async_files_from_dir
+
+
+@pytest.fixture
+def skill(tmp_path: Path) -> Path:
+    directory = tmp_path / "greeting"
+    (directory / "scripts").mkdir(parents=True)
+    (directory / "SKILL.md").write_text("# hi\n")
+    (directory / "scripts" / "run.py").write_text("print(1)\n")
+    return directory
+
+
+def _names(files: list[object]) -> list[str]:
+    return sorted(name for name, *_ in files)  # type: ignore[misc]
+
+
+EXPECTED = ["greeting/SKILL.md", "greeting/scripts/run.py"]
+
+
+def test_names_carry_the_directory(skill: Path) -> None:
+    assert _names(files_from_dir(skill)) == EXPECTED
+
+
+RELATIVE = [("inside", "."), ("inside", "./"), ("inside", "../greeting"), ("parent", "greeting")]
+
+
+def test_a_relative_root_names_the_same_files(skill: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    # the names go to the API as given, so `.` must not drop the directory and
+    # `..` must not reach a name
+    for where, spelling in RELATIVE:
+        monkeypatch.chdir(skill if where == "inside" else skill.parent)
+        assert _names(files_from_dir(spelling)) == EXPECTED, spelling
+
+
+def test_a_trailing_separator_changes_nothing(skill: Path) -> None:
+    assert _names(files_from_dir(f"{skill}{os.sep}")) == EXPECTED
+
+
+async def test_async_names_carry_the_directory(skill: Path) -> None:
+    assert _names(await async_files_from_dir(skill)) == EXPECTED
+
+
+async def test_async_a_relative_root_names_the_same_files(skill: Path, monkeypatch: pytest.MonkeyPatch) -> None:
+    for where, spelling in RELATIVE:
+        monkeypatch.chdir(skill if where == "inside" else skill.parent)
+        assert _names(await async_files_from_dir(spelling)) == EXPECTED, spelling