diff --git a/config.h b/config.h
index e3ad964b..4e7e6b60 100644
--- a/config.h
+++ b/config.h
@@ -34,6 +34,7 @@
 #  define __BSD_VISIBLE 1
 #  define HAVE_NETINET_IN_H
 #else
+#  define _XOPEN_SOURCE 700
 #  define _DEFAULT_SOURCE 1
 #  define _POSIX_C_SOURCE 200809L
 #endif