diff --git a/src/window_func.h b/src/window_func.h
--- a/src/window_func.h
+++ b/src/window_func.h
@@ -40,6 +40,7 @@ void InvalidateWindowClassesData(WindowC
 
 void DeleteNonVitalWindows();
 void DeleteAllNonVitalWindows();
+void DeleteAllMessages();
 void DeleteConstructionWindows();
 void HideVitalWindows();
 void ShowVitalWindows();