diff --git a/src/google/adk/tools/google_api_tool/google_api_tool.py b/src/google/adk/tools/google_api_tool/google_api_tool.py
index b51f13f5..04d1ebb4 100644
--- a/src/google/adk/tools/google_api_tool/google_api_tool.py
+++ b/src/google/adk/tools/google_api_tool/google_api_tool.py
@@ -39,6 +39,7 @@ class GoogleApiTool(BaseTool):
       client_id: Optional[str] = None,
       client_secret: Optional[str] = None,
       service_account: Optional[ServiceAccount] = None,
+      *,
       additional_headers: Optional[Dict[str, str]] = None,
   ):
     super().__init__(
diff --git a/src/google/adk/tools/google_api_tool/google_api_toolset.py b/src/google/adk/tools/google_api_tool/google_api_toolset.py
index 5127f66d..714e6542 100644
--- a/src/google/adk/tools/google_api_tool/google_api_toolset.py
+++ b/src/google/adk/tools/google_api_tool/google_api_toolset.py
@@ -59,6 +59,7 @@ class GoogleApiToolset(BaseToolset):
       tool_filter: Optional[Union[ToolPredicate, List[str]]] = None,
       service_account: Optional[ServiceAccount] = None,
       tool_name_prefix: Optional[str] = None,
+      *,
       additional_headers: Optional[Dict[str, str]] = None,
   ):
     super().__init__(tool_filter=tool_filter, tool_name_prefix=tool_name_prefix)
@@ -81,7 +82,7 @@ class GoogleApiToolset(BaseToolset):
             self._client_id,
             self._client_secret,
             self._service_account,
-            self._additional_headers,
+            additional_headers=self._additional_headers,
         )
         for tool in await self._openapi_toolset.get_tools(readonly_context)
         if self._is_tool_selected(tool, readonly_context)
diff --git a/tests/unittests/tools/google_api_tool/test_google_api_toolset.py b/tests/unittests/tools/google_api_tool/test_google_api_toolset.py
index f8cf756c..5da0cb4b 100644
--- a/tests/unittests/tools/google_api_tool/test_google_api_toolset.py
+++ b/tests/unittests/tools/google_api_tool/test_google_api_toolset.py
@@ -214,7 +214,11 @@ class TestGoogleApiToolset:
 
     for i, rest_tool in enumerate(mock_rest_api_tools):
       mock_google_api_tool_class.assert_any_call(
-          rest_tool, client_id, client_secret, sa_mock, additional_headers
+          rest_tool,
+          client_id,
+          client_secret,
+          sa_mock,
+          additional_headers=additional_headers,
       )
       assert tools[i] is mock_google_api_tool_instances[i]