diff --git a/readline/readline-4.3/display.c b/readline/readline-4.3/display.c
index 83f12f26..ab6e39b1 100644
--- a/readline/readline-4.3/display.c
+++ b/readline/readline-4.3/display.c
@@ -21,6 +21,8 @@
    59 Temple Place, Suite 330, Boston, MA 02111 USA. */
 #define READLINE_LIBRARY
 
+#define _XOPEN_SOURCE       /* See feature_test_macros(7) */
+
 #if defined (HAVE_CONFIG_H)
 #  include <config.h>
 #endif
@@ -41,7 +43,6 @@
 
 #include <stdio.h>
 
-#define _XOPEN_SOURCE       /* See feature_test_macros(7) */
 #include <wchar.h>
 
 /* System-specific feature definitions and include files. */
diff --git a/readline/readline-4.3/mbutil.c b/readline/readline-4.3/mbutil.c
index 397c22a6..32cbee1f 100644
--- a/readline/readline-4.3/mbutil.c
+++ b/readline/readline-4.3/mbutil.c
@@ -25,6 +25,8 @@
 #  include <config.h>
 #endif
 
+#define _XOPEN_SOURCE       /* See feature_test_macros(7) */
+
 #include <sys/types.h>
 #include <fcntl.h>
 #include <wchar.h>