diff --git a/include/GL/glfw3.h b/include/GL/glfw3.h
index 955086af..32c3899a 100644
--- a/include/GL/glfw3.h
+++ b/include/GL/glfw3.h
@@ -173,6 +173,10 @@ extern "C" {
   #endif
 #endif
 
+/* This is needed for the declaration of size_t.
+ */
+#include <stddef.h>
+
 
 /*************************************************************************
  * GLFW version