diff --git a/ChangeLog b/ChangeLog
index 4b5b1315b3..8dc6e47b19 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+Fri Mar 16 16:21:35 2007  Akinori MUSHA  <knu@iDaemons.org>
+
+	* ext/thread/thread.c (wait_condvar, lock_mutex): Fix a problem in
+	  ConditionVariable#wait that occurs when two threads that are
+	  trying to access the condition variable are also in concurrence
+	  for the given mutex; submitted by: Sylvain Joyeux
+	  <sylvain.joyeux AT m4x.org> and MenTaLguY <mental AT rydia.net>
+	  in [ruby-core:10598].
+
 Fri Mar 16 16:17:27 2007  Akinori MUSHA  <knu@iDaemons.org>
 
 	* test/thread/test_thread.rb: Add a test script for the `thread'
diff --git a/ext/thread/thread.c b/ext/thread/thread.c
index e9dde37a18..54681a8c90 100644
--- a/ext/thread/thread.c
+++ b/ext/thread/thread.c
@@ -390,7 +390,7 @@ rb_mutex_try_lock(VALUE self)
  *
  */
 
-static void
+static VALUE
 lock_mutex(Mutex *mutex)
 {
     VALUE current;
@@ -405,6 +405,7 @@ lock_mutex(Mutex *mutex)
     mutex->owner = current; 
 
     rb_thread_critical = 0;
+    return Qnil;
 }
 
 static VALUE
@@ -623,18 +624,12 @@ static void
 wait_condvar(ConditionVariable *condvar, Mutex *mutex)
 {
     rb_thread_critical = 1;
-    if (!RTEST(mutex->owner)) {
+    if (rb_thread_current() != mutex->owner) {
         rb_thread_critical = 0;
-        return;
+        rb_raise(rb_eThreadError, "not owner of the synchronization mutex");
     }
-    if (mutex->owner != rb_thread_current()) {
-        rb_thread_critical = 0;
-        rb_raise(rb_eThreadError, "Not owner");
-    }
-    mutex->owner = Qnil;
-    wait_list(&condvar->waiting);
-
-    lock_mutex(mutex);
+    unlock_mutex_inner(mutex);
+    rb_ensure(wait_list, (VALUE)&condvar->waiting, lock_mutex, (VALUE)mutex);
 }
 
 static VALUE