diff --git a/Fltk/openglWindow.cpp b/Fltk/openglWindow.cpp
index d453c4d1deae01fde35c7d9f5cd3b658705eff18..923fa83a3386db92e73859df248edb8ba6f922c1 100644
--- a/Fltk/openglWindow.cpp
+++ b/Fltk/openglWindow.cpp
@@ -4,6 +4,7 @@
 // bugs and problems to <gmsh@geuz.org>.
 
 #include <stdio.h>
+#include <string.h>
 #include "openglWindow.h"
 #include "graphicWindow.h"
 #include "manipWindow.h"