diff --git a/src/libstrongswan/utils/lexparser.c b/src/libstrongswan/utils/lexparser.c
index 52a0e1617..35ba0d7a6 100644
--- a/src/libstrongswan/utils/lexparser.c
+++ b/src/libstrongswan/utils/lexparser.c
@@ -21,6 +21,8 @@
  * RCSID $Id$
  */
 
+/* memrchr is a GNU extension */
+#define _GNU_SOURCE
 #include <string.h>
 
 #include "lexparser.h"