diff --git a/COMTool/plugins/protocols.py b/COMTool/plugins/protocols.py
index 024a20e..f96d511 100644
--- a/COMTool/plugins/protocols.py
+++ b/COMTool/plugins/protocols.py
@@ -29,7 +29,7 @@ def decode(data:bytes) -> bytes:
     return data
 
 def encode(data:bytes) -> bytes:
-    return data + bytes([sum(a) % 256])
+    return data + bytes([sum(data) % 256])
 '''