diff --git a/src/ATC/ATCdisplay.hxx b/src/ATC/ATCdisplay.hxx
index c41bb72f8..0734e446f 100644
--- a/src/ATC/ATCdisplay.hxx
+++ b/src/ATC/ATCdisplay.hxx
@@ -76,7 +76,7 @@ public:
 
     // Register a single message for display after a delay of delay seconds
     // Will automatically stop displaying after a suitable interval.
-    void RegisterSingleMessage(string msg, double delay);	// OK - I know passing a string in and out is probably not good but it will have to do for now.
+    void RegisterSingleMessage(string msg, double delay = 0.0);	// OK - I know passing a string in and out is probably not good but it will have to do for now.
 
     // For now we will assume only one repeating message at once
     // This is not really robust