diff --git a/src/js/serial_backend.js b/src/js/serial_backend.js
index b8d17283da..10067c8296 100644
--- a/src/js/serial_backend.js
+++ b/src/js/serial_backend.js
@@ -150,7 +150,7 @@ export function initializeSerialBackend() {
                         finishClose(toggleStatus);
                     }
 
-                    mspHelper.setArmingEnabled(true, false, onFinishCallback);
+                    mspHelper?.setArmingEnabled(true, false, onFinishCallback);
                 }
             }
         }