diff --git a/tests/mock_smbus2.py b/tests/mock_smbus2.py
index bdd8d20..744c615 100644
--- a/tests/mock_smbus2.py
+++ b/tests/mock_smbus2.py
@@ -40,7 +40,8 @@ class MockSMBus:
         for i in range(len(s.status)):
             msg.buf[i]=chr(s.status[i])
             if s._break_crc and i%3 == 2:
-                msg.buf[i]=msg.buf[i]^42
+                msg.buf[i]=chr(s.status[i]^42)
+        self.status=None
                 
 
     def _process_write(s,msg):