diff --git a/radio/src/gui/gui_common_arm.cpp b/radio/src/gui/gui_common_arm.cpp
index aaeba662c..8a252aa3f 100644
--- a/radio/src/gui/gui_common_arm.cpp
+++ b/radio/src/gui/gui_common_arm.cpp
@@ -131,6 +131,9 @@ int getChannelsUsed()
 
 bool isSourceAvailable(int source)
 {
+  if (source < 0)
+    return false;
+
   if (source>=MIXSRC_FIRST_INPUT && source<=MIXSRC_LAST_INPUT) {
     return isInputAvailable(source - MIXSRC_FIRST_INPUT);
   }