diff --git a/ext/sockets/config.m4 b/ext/sockets/config.m4
index d4f92082c3b2d..aafedcb99ddd3 100644
--- a/ext/sockets/config.m4
+++ b/ext/sockets/config.m4
@@ -67,6 +67,9 @@ if test "$PHP_SOCKETS" != "no"; then
   AC_CACHE_CHECK([if ancillary credentials uses ucred],[ac_cv_ucred],
   [
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
 #include <sys/socket.h>
   ]], [[struct ucred u = {.gid = 0};]])],
       [ac_cv_ucred=yes], [ac_cv_ucred=no])