diff --git a/ChangeLog b/ChangeLog
index 80925f5867..24548e2d13 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Oct 15 22:08:37 2014  Tanaka Akira  <akr@fsij.org>
+
+	* ext/etc/etc.c (etc_nprocessors_affin): Test CPU_ALLOC availability.
+	  CentOS 5 don't have CPU_ALLOC().
+
 Wed Oct 15 18:26:19 2014  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* ext/etc/etc.c (etc_nprocessors_affinity): use sched_getaffinity
diff --git a/ext/etc/etc.c b/ext/etc/etc.c
index aaa5025a9c..4a4df3654a 100644
--- a/ext/etc/etc.c
+++ b/ext/etc/etc.c
@@ -909,7 +909,7 @@ io_pathconf(VALUE io, VALUE arg)
 
 #if (defined(HAVE_SYSCONF) && defined(_SC_NPROCESSORS_ONLN)) || defined(_WIN32)
 
-#ifdef HAVE_SCHED_GETAFFINITY
+#if defined(HAVE_SCHED_GETAFFINITY) && defined(CPU_ALLOC)
 static int
 etc_nprocessors_affin(void)
 {
@@ -987,7 +987,7 @@ etc_nprocessors(VALUE obj)
 
 #if !defined(_WIN32)
 
-#ifdef HAVE_SCHED_GETAFFINITY
+#if defined(HAVE_SCHED_GETAFFINITY) && defined(CPU_ALLOC)
     int ncpus;
 
     ncpus = etc_nprocessors_affin();