diff --git a/build/config/sched_setaffinity.m4 b/build/config/sched_setaffinity.m4
index ac81896fcd..9e4bb67beb 100644
--- a/build/config/sched_setaffinity.m4
+++ b/build/config/sched_setaffinity.m4
@@ -8,7 +8,7 @@ AC_CHECK_FUNCS(sched_setaffinity sched_getaffinity)
         AC_CACHE_CHECK([whether the CPU_SET and CPU_ZERO macros are defined],
         ac_cv_cpu_set_defined,[
 	saved_CFLAGS="$CFLAGS"
-	CFLAGS="$CFLAGS $SWITCH_AM_CFLAGS"
+	CFLAGS="$CFLAGS $SWITCH_AM_CFLAGS $SWITCH_ANSI_CFLAGS -D_GNU_SOURCE"
         AC_TRY_COMPILE( [#include <sched.h>],[ cpu_set_t t; CPU_ZERO(&t); CPU_SET(1,&t); ],
 	        ac_cv_cpu_set_defined=yes,ac_cv_cpu_set_defined=no)])
         if test "$ac_cv_cpu_set_defined" = "yes" ; then