diff --git a/libraries/libldap_r/thr_posix.c b/libraries/libldap_r/thr_posix.c
index 3ea3d16f60..b2cebaeb76 100644
--- a/libraries/libldap_r/thr_posix.c
+++ b/libraries/libldap_r/thr_posix.c
@@ -14,14 +14,16 @@
  * <http://www.OpenLDAP.org/license.html>.
  */
 
-#ifndef _GNU_SOURCE
-#define _GNU_SOURCE 1		/* For pthread_setconcurrency() on glibc */
-#endif
 
 #include "portable.h"
 
 #if defined( HAVE_PTHREADS )
 
+#ifdef __GLIBC__
+#undef _FEATURES_H
+#define _XOPEN_SOURCE 500		/* For pthread_setconcurrency() on glibc */
+#endif
+
 #include <ac/errno.h>
 
 #ifdef REPLACE_BROKEN_YIELD