diff --git a/ChangeLog b/ChangeLog
index 0ca0cff4bc..f766c11273 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Sat May  7 18:28:37 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* thread_pthread.c (USE_MONOTONIC_COND): check the availability
+	  more strictly.
+
+	* thread_pthread.h (rb_thread_cond_t): ditto.
+
 Sat May  7 15:18:06 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 	fix incorrect native_cond_signal call when deadlock was detected.
 
diff --git a/thread_pthread.c b/thread_pthread.c
index 866caac9d0..8554414a1c 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -30,8 +30,11 @@ static void native_cond_destroy(rb_thread_cond_t *cond);
 
 #define RB_CONDATTR_CLOCK_MONOTONIC 1
 
-#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined(CLOCK_MONOTONIC) && defined(HAVE_CLOCK_GETTIME)
+#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK) && defined(HAVE_CLOCKID_T) && \
+    defined(CLOCK_REALTIME) && defined(CLOCK_MONOTONIC) && defined(HAVE_CLOCK_GETTIME)
 #define USE_MONOTONIC_COND 1
+#else
+#define USE_MONOTONIC_COND 0
 #endif
 
 #define GVL_SIMPLE_LOCK 0
@@ -230,10 +233,10 @@ native_cond_initialize(rb_thread_cond_t *cond, int flags)
     int r;
     pthread_condattr_t attr;
 
-    cond->clockid = CLOCK_REALTIME;
     pthread_condattr_init(&attr);
 
 #if USE_MONOTONIC_COND
+    cond->clockid = CLOCK_REALTIME;
     if (flags & RB_CONDATTR_CLOCK_MONOTONIC) {
 	r = pthread_condattr_setclock(&attr, CLOCK_MONOTONIC);
 	if (r == 0) {
@@ -323,10 +326,10 @@ native_cond_timeout(rb_thread_cond_t *cond, struct timespec timeout_rel)
 	    rb_sys_fail("clock_gettime()");
 	goto out;
     }
-#endif
 
     if (cond->clockid != CLOCK_REALTIME)
 	rb_bug("unsupported clockid %d", cond->clockid);
+#endif
 
     ret = gettimeofday(&tv, 0);
     if (ret != 0)
diff --git a/thread_pthread.h b/thread_pthread.h
index 64a17fcf67..97a26e0e80 100644
--- a/thread_pthread.h
+++ b/thread_pthread.h
@@ -20,7 +20,9 @@ typedef pthread_mutex_t rb_thread_lock_t;
 
 typedef struct rb_thread_cond_struct {
     pthread_cond_t cond;
+#ifdef HAVE_CLOCKID_T
     clockid_t clockid;
+#endif
 } rb_thread_cond_t;
 
 typedef struct native_thread_data_struct {