diff --git a/requirements.txt b/requirements.txt
index 66137198..4f68c40d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -18,4 +18,5 @@ rqdatac
 ta-lib
 ibapi
 deap
-pyzmq
\ No newline at end of file
+pyzmq
+wmi
\ No newline at end of file
diff --git a/vnpy/rpc/__init__.py b/vnpy/rpc/__init__.py
index b74e1f4e..f29bc00b 100644
--- a/vnpy/rpc/__init__.py
+++ b/vnpy/rpc/__init__.py
@@ -239,7 +239,7 @@ class RpcClient:
 
     def join(self):
         # Wait for RpcClient thread to exit
-        if self.__thread.isAlive():
+        if self.__thread and self.__thread.is_alive():
             self.__thread.join()
         self.__thread = None