diff --git a/src/openai/_base_client.py b/src/openai/_base_client.py
index a168301f75..7b03d26f7a 100644
--- a/src/openai/_base_client.py
+++ b/src/openai/_base_client.py
@@ -578,7 +578,10 @@ def base_url(self) -> URL:
 
     @base_url.setter
     def base_url(self, url: URL | str) -> None:
-        self._client.base_url = url if isinstance(url, URL) else URL(url)
+        url = url if isinstance(url, URL) else URL(url)
+        url = self._enforce_trailing_slash(url)
+        self._base_url = url
+        self._client.base_url = url
 
     @lru_cache(maxsize=None)
     def platform_headers(self) -> Dict[str, str]:
diff --git a/tests/test_client.py b/tests/test_client.py
index c5dbfe4bfe..5cd22912d7 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -986,6 +986,12 @@ def test_base_url_env(self) -> None:
             client = AsyncOpenAI(api_key=api_key, _strict_response_validation=True)
             assert client.base_url == "http://localhost:5000/from/env/"
 
+    def test_change_base_url(selr) -> None:
+        with update_env(OPENAI_BASE_URL="http://localhost:5000/from/env"):
+            client = AsyncOpenAI(api_key=api_key, _strict_response_validation=True)
+            client.base_url = "http://localhost:5000/custom/path/"
+            assert client.base_url == "http://localhost:5000/custom/path/"
+
     @pytest.mark.parametrize(
         "client",
         [