diff --git a/src/drivers/X11/Fl_X11_Screen_Driver.h b/src/drivers/X11/Fl_X11_Screen_Driver.h
index b699a9ac4..4a4667cf5 100644
--- a/src/drivers/X11/Fl_X11_Screen_Driver.h
+++ b/src/drivers/X11/Fl_X11_Screen_Driver.h
@@ -53,7 +53,7 @@ public:
   // --- audible output
   virtual void beep(int type);
   // --- global events
-  virtual void flush() = 0;
+  virtual void flush();
 };