diff --git a/Firmware/mmu2_protocol_logic.cpp b/Firmware/mmu2_protocol_logic.cpp
index 1970bc792..d8cca0fd4 100644
--- a/Firmware/mmu2_protocol_logic.cpp
+++ b/Firmware/mmu2_protocol_logic.cpp
@@ -378,7 +378,7 @@ StepStatus Idle::Step() {
             }
             break;
         default:
-            break;
+            return ProtocolError;
         }
         SendFINDAQuery();
         return Processing;