diff --git a/rcon/readline.py b/rcon/readline.py
index db75bc5..e2a0e6d 100644
--- a/rcon/readline.py
+++ b/rcon/readline.py
@@ -49,4 +49,4 @@ else:
             return self
 
         def __exit__(self, *_):
-            pass
+            return None     # Mockup for non-posix systems.