diff --git a/sisyphus/manager.py b/sisyphus/manager.py
index 93ebd9a..6c1784d 100644
--- a/sisyphus/manager.py
+++ b/sisyphus/manager.py
@@ -45,7 +45,8 @@ def f(job):
 
     def close(self):
         self.stopped.set()
-        self.join()
+        if self.is_alive():
+            self.join()
         self.thread_pool.close()