diff --git a/httpx/_client.py b/httpx/_client.py
index 2249231f8c..6131f14df9 100644
--- a/httpx/_client.py
+++ b/httpx/_client.py
@@ -281,7 +281,7 @@ def auth(self) -> Auth | None:
         return self._auth
 
     @auth.setter
-    def auth(self, auth: AuthTypes) -> None:
+    def auth(self, auth: AuthTypes | None) -> None:
         self._auth = self._build_auth(auth)
 
     @property
diff --git a/tests/client/test_auth.py b/tests/client/test_auth.py
index 7638b8bd68..5c5665f080 100644
--- a/tests/client/test_auth.py
+++ b/tests/client/test_auth.py
@@ -335,6 +335,24 @@ async def test_auth_property() -> None:
         assert response.json() == {"auth": "Basic dXNlcjpwYXNzd29yZDEyMw=="}
 
 
+@pytest.mark.anyio
+async def test_auth_property_none() -> None:
+    app = App()
+
+    async with httpx.AsyncClient(
+        transport=httpx.MockTransport(app), auth=("user", "password123")
+    ) as client:
+        assert isinstance(client.auth, httpx.BasicAuth)
+
+        client.auth = None
+        assert client.auth is None
+
+        url = "https://example.org/"
+        response = await client.get(url)
+        assert response.status_code == 200
+        assert response.json() == {"auth": None}
+
+
 @pytest.mark.anyio
 async def test_auth_invalid_type() -> None:
     app = App()