diff -urNad gmsh-2.1.1.orig/Fltk/Message.cpp gmsh-2.1.1/Fltk/Message.cpp
--- gmsh-2.1.1.orig/Fltk/Message.cpp	2008-04-10 02:47:58.000000000 +0100
+++ gmsh-2.1.1/Fltk/Message.cpp	2008-04-10 02:54:51.000000000 +0100
@@ -20,6 +20,7 @@
 // Please report all bugs and problems to <gmsh@geuz.org>.
 
 #include <string.h>
+#include <cstdlib>
 #include <signal.h>
 #include "Message.h"
 #include "GmshUI.h"