diff --git a/src/google/adk/tools/mcp_tool/session_context.py b/src/google/adk/tools/mcp_tool/session_context.py
index 2080588c33..e0ffa93e47 100644
--- a/src/google/adk/tools/mcp_tool/session_context.py
+++ b/src/google/adk/tools/mcp_tool/session_context.py
@@ -239,7 +239,7 @@ async def close(self):
     except Exception as e:
       logger.warning(f'Failed to close MCP session: {e}')
 
-  async def __aenter__(self) -> ClientSession:
+  async def __a_enter__(self) -> ClientSession:
     return await self.start()
 
   async def __aexit__(self, exc_type, exc_val, exc_tb):