diff --git a/config.m4 b/config.m4
index ada2e983ba..701eaa569a 100644
--- a/config.m4
+++ b/config.m4
@@ -183,6 +183,7 @@ AC_DEFUN([AC_SWOOLE_CPU_AFFINITY],
         #include <sys/cpuset.h>
         typedef cpuset_t cpu_set_t;
         #else
+        #define _GNU_SOURCE 1
         #include <sched.h>
         #endif
     ]], [[