diff --git a/protocol/hp_ipp.c b/protocol/hp_ipp.c
index 7853201..41892c6 100644
--- a/protocol/hp_ipp.c
+++ b/protocol/hp_ipp.c
@@ -18,6 +18,7 @@ Boston, MA 02110-1301, USA.
 
 \******************************************************************************/
 
+#define _GNU_SOURCE
 #include <cups/cups.h>
 #include <cups/language.h>
 #include <cups/ppd.h>