diff --git a/dockerfiles/cache-downloader/cache-downloader.py b/dockerfiles/cache-downloader/cache-downloader.py
index 49f4367..0e6fd6d 100644
--- a/dockerfiles/cache-downloader/cache-downloader.py
+++ b/dockerfiles/cache-downloader/cache-downloader.py
@@ -19,6 +19,12 @@ def download_dependency(
     version_path = os.path.join(BASE_PATH, release_name, f"python{python_version}")
     done_file = os.path.join(version_path, f"{python_version}-done")
 
+    if Path(done_file).is_file():
+        print(
+            f"{datetime.datetime.now()}: {release_name} python{python_version} already cached, skipping download"
+        )
+        return
+
     # Create the version directory if it doesn't exist
     os.makedirs(version_path, exist_ok=True)
 
@@ -57,7 +63,7 @@ def download_dependency(
         f"{datetime.datetime.now()}: Done downloading {release_name} {s3_path} and extracting to {version_path}"
     )
     # Create the "done" file
-    open(done_file, "a").close()
+    Path(done_file).touch()
 
 
 def submit_downloading(
diff --git a/tests/unit/test_cache_downloader.py b/tests/unit/test_cache_downloader.py
index 485727d..2e09a58 100644
--- a/tests/unit/test_cache_downloader.py
+++ b/tests/unit/test_cache_downloader.py
@@ -1,7 +1,7 @@
 import importlib.util
 import os
 import shutil
-from unittest.mock import patch
+from unittest.mock import MagicMock, patch
 
 import pytest
 
@@ -21,6 +21,7 @@
 _spec.loader.exec_module(_mod)
 
 cleanup_old_versions = _mod.cleanup_old_versions
+download_dependency = _mod.download_dependency
 
 
 class TestCleanupOldVersions:
@@ -169,3 +170,48 @@ def _fail_on_v1(path, *args, **kwargs):
         assert (tmp_path / "v1").exists()
         assert (tmp_path / "v2").exists()
         assert (tmp_path / "v3").exists()
+
+
+class TestDownloadDependency:
+    def test_skips_download_when_done_file_exists(self, tmp_path):
+        """Already-cached version should not trigger a download."""
+        release = "v1.0.0"
+        py_ver = "3.11"
+        version_path = tmp_path / release / f"python{py_ver}"
+        version_path.mkdir(parents=True)
+        (version_path / f"{py_ver}-done").write_text("ok")
+
+        with (
+            patch.object(_mod, "BASE_PATH", str(tmp_path)),
+            patch.object(_mod.subprocess, "Popen") as mock_popen,
+        ):
+            download_dependency(release, py_ver, "fake-bucket")
+
+        mock_popen.assert_not_called()
+
+    def test_downloads_when_done_file_missing(self, tmp_path):
+        """Missing done file should trigger the download."""
+        release = "v1.0.0"
+        py_ver = "3.11"
+        version_path = tmp_path / release / f"python{py_ver}"
+        version_path.mkdir(parents=True)
+
+        mock_aws = MagicMock()
+        mock_aws.stdout = MagicMock()
+        mock_aws.stderr = MagicMock(read=MagicMock(return_value=b""))
+        mock_aws.wait.return_value = 0
+
+        mock_tar = MagicMock()
+        mock_tar.communicate.return_value = (b"", b"")
+        mock_tar.returncode = 0
+
+        with (
+            patch.object(_mod, "BASE_PATH", str(tmp_path)),
+            patch.object(
+                _mod.subprocess, "Popen", side_effect=[mock_aws, mock_tar]
+            ) as mock_popen,
+        ):
+            download_dependency(release, py_ver, "fake-bucket")
+
+        assert mock_popen.call_count == 2
+        assert (version_path / f"{py_ver}-done").exists()