diff --git a/src/system.cpp b/src/system.cpp
index 7bb76f310..712665a92 100644
--- a/src/system.cpp
+++ b/src/system.cpp
@@ -717,6 +717,8 @@ bool System::check_upgrade() {
 
     Serial.end();
     return true;
+#else
+    return false;
 #endif
 }