=== modified file 'mandos'
--- mandos	2019-09-01 04:27:59 +0000
+++ mandos	2019-09-03 18:43:11 +0000
@@ -1053,7 +1053,8 @@
         # Read return code from connection (see call_pipe)
         returncode = connection.recv()
         connection.close()
-        self.checker.join()
+        if self.checker is not None:
+            self.checker.join()
         self.checker_callback_tag = None
         self.checker = None