diff --git a/src/ATC/ATCDialog.cxx b/src/ATC/ATCDialog.cxx
index d24b1b024..b2b6964cd 100644
--- a/src/ATC/ATCDialog.cxx
+++ b/src/ATC/ATCDialog.cxx
@@ -264,7 +264,8 @@ void FGATCDialog::PopupCallback(int num) {
 		//cout << "TOWER " << endl;
 		//cout << "ident is " << atcptr->get_ident() << endl;
 		atcmentry_vec_type atcmlist = (available_dialog[TOWER])[atcptr->get_ident()];
-		if(atcmlist.size()) {
+		unsigned int size = atcmlist.size();
+		if(size && num < size) {
 			//cout << "Doing callback...\n";
 			ATCMenuEntry a = atcmlist[num];
 			atcptr->SetFreqInUse();