diff --git a/include/chameleon.h b/include/chameleon.h
index 253767cbb86d28adf7acc00a4b21d3edb935af39..03bf38843c710608143e67ffabe44b3fe504aede 100644
--- a/include/chameleon.h
+++ b/include/chameleon.h
@@ -28,6 +28,7 @@
  * CHAMELEON types and constants
  */
 #include "chameleon/config.h"
+#define _GNU_SOURCE 1
 #include <stdio.h>
 #include "chameleon/constants.h"
 #include "chameleon/types.h"