diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index 9dfab2e..058ce22 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -17,6 +17,17 @@ env:
   AWS_REGION: eu-west-1
 
 jobs:
+  windows-private-files:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: astral-sh/setup-uv@v7
+      - uses: actions/setup-python@v6
+        with:
+          python-version: '3.12'
+      - name: Verify Windows credential file ACLs
+        run: uv run --with pytest pytest --noconftest -q tests/test_private_files.py
+
   test:
     runs-on: ubuntu-latest
     steps:
diff --git a/src/dapier/private_files.py b/src/dapier/private_files.py
index 022ede6..128cabd 100644
--- a/src/dapier/private_files.py
+++ b/src/dapier/private_files.py
@@ -5,9 +5,18 @@
 
 def _windows_acl(path, script):
     env = dict(os.environ, DAPIER_PRIVATE_PATH=os.fspath(path))
+    # A Python child of PowerShell 7 inherits its module paths. Windows
+    # PowerShell must load its own Security module, not the incompatible
+    # version from the parent shell's PSModulePath.
+    bootstrap = (
+        "$ErrorActionPreference = 'Stop'; "
+        "Import-Module (Join-Path $PSHOME "
+        "'Modules\\Microsoft.PowerShell.Security\\Microsoft.PowerShell.Security.psd1') "
+        "-ErrorAction Stop; "
+    )
     return subprocess.run(
         ["powershell.exe", "-NoProfile", "-NonInteractive", "-Command",
-         "$ErrorActionPreference = 'Stop'; " + script],
+         bootstrap + script],
         env=env, capture_output=True, text=True, check=True,
     ).stdout.strip()
 
diff --git a/tests/test_private_files.py b/tests/test_private_files.py
index 2a12e41..9b49e43 100644
--- a/tests/test_private_files.py
+++ b/tests/test_private_files.py
@@ -20,13 +20,38 @@ def test_shared_token_is_rejected(tmp_path):
     protect(path)
     if os.name == "nt":
         _windows_acl(path, """
-            $acl = Get-Acl -LiteralPath $env:DAPIER_PRIVATE_PATH
+            $acl = [System.IO.File]::GetAccessControl($env:DAPIER_PRIVATE_PATH, [System.Security.AccessControl.AccessControlSections]::Access)
             $sid = New-Object System.Security.Principal.SecurityIdentifier('S-1-1-0')
             $rule = New-Object System.Security.AccessControl.FileSystemAccessRule($sid, 'Read', 'Allow')
             $acl.AddAccessRule($rule)
-            Set-Acl -LiteralPath $env:DAPIER_PRIVATE_PATH -AclObject $acl
+            [System.IO.File]::SetAccessControl($env:DAPIER_PRIVATE_PATH, $acl)
         """)
     else:
         os.chmod(path, 0o644)
     with pytest.raises(ValueError, match="owner-only"):
         require_private(path)
+
+
+@pytest.mark.skipif(os.name != "nt", reason="Windows PowerShell module resolution")
+def test_acl_ignores_incompatible_inherited_security_module(tmp_path, monkeypatch):
+    """A parent shell's module directory must not break credential privacy."""
+    modules = tmp_path / "parent-shell-modules"
+    security = modules / "Microsoft.PowerShell.Security"
+    security.mkdir(parents=True)
+    (security / "Microsoft.PowerShell.Security.psd1").write_text(
+        "@{ ModuleVersion = '99.0.0'; RootModule = 'incompatible.psm1'; "
+        "GUID = 'ee0c3554-2ffd-4474-b7eb-ad6cef54dce8' }"
+    )
+    (security / "incompatible.psm1").write_text(
+        "throw 'The parent shell Security module cannot run in this process'"
+    )
+    monkeypatch.setenv(
+        "PSModulePath", str(modules) + os.pathsep + os.environ.get("PSModulePath", "")
+    )
+    path = tmp_path / "token with spaces and 'quotes'.txt"
+    path.write_text("synthetic credential")
+
+    protect(path)
+    require_private(path)
+
+    assert path.read_text() == "synthetic credential"