diff --git a/internal_filesystem/lib/mpos/board/odroid_go.py b/internal_filesystem/lib/mpos/board/odroid_go.py
index 4aa1d946..70db69d7 100644
--- a/internal_filesystem/lib/mpos/board/odroid_go.py
+++ b/internal_filesystem/lib/mpos/board/odroid_go.py
@@ -73,7 +73,7 @@ class BuzzerCallbacks:
         print("Unmute buzzer")
         self.dac_pin.value(1)  # Unmute
 
-    def mute(self):
+    def mute(self, unused=None): # This is used as rtttl's on_complete function, which passes a string message argument
         print("Mute buzzer")
         self.dac_pin.value(0)  # Mute