diff --git a/src/openai/__init__.py b/src/openai/__init__.py
index b2093ada68..d37315a9d9 100644
--- a/src/openai/__init__.py
+++ b/src/openai/__init__.py
@@ -204,7 +204,7 @@ def webhook_secret(self, value: str | None) -> None:  # type: ignore
     @override
     def base_url(self) -> _httpx.URL:
         if base_url is not None:
-            return _httpx.URL(base_url)
+            return self._enforce_trailing_slash(_httpx.URL(base_url))
 
         return super().base_url
 
diff --git a/tests/test_module_client.py b/tests/test_module_client.py
index 9c9a1addab..2d5a928c60 100644
--- a/tests/test_module_client.py
+++ b/tests/test_module_client.py
@@ -42,8 +42,15 @@ def test_base_url_option() -> None:
 
     openai.base_url = "http://foo.com"
 
-    assert openai.base_url == URL("http://foo.com")
-    assert openai.completions._client.base_url == URL("http://foo.com")
+    assert openai.base_url == "http://foo.com"
+    assert openai.completions._client.base_url.raw_path == b"/"
+
+
+def test_base_url_option_without_trailing_slash() -> None:
+    openai.base_url = "http://foo.com/custom/path"
+
+    assert openai.base_url == "http://foo.com/custom/path"
+    assert openai.completions._client.base_url == URL("http://foo.com/custom/path/")
 
 
 def test_timeout_option() -> None: