diff --git a/libraries/liblutil/getpeereid.c b/libraries/liblutil/getpeereid.c
index bf38ff362e..adfec14af9 100644
--- a/libraries/liblutil/getpeereid.c
+++ b/libraries/liblutil/getpeereid.c
@@ -14,7 +14,9 @@
  * <http://www.OpenLDAP.org/license.html>.
  */
 
-#define _GNU_SOURCE
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE 1			/* Needed for glibc struct ucred */
+#endif
 
 #include "portable.h"