diff --git a/ChangeLog b/ChangeLog
index 5f719aaae7..b9207b80fa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Wed Oct  6 11:52:12 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (fptr_finalize): write_mutex might have been destroyed
+	  already in finalization phase, as the order of finalizers is not
+	  guaranteed.  rb_mutex_t should be used in place of Mutex object
+	  in the future.
+
 Tue Oct  5 22:17:02 2010  wanabe  <s.wanabe@gmail.com>
 
 	* win32/mkexports.rb: revert r29320 and r29402.
diff --git a/io.c b/io.c
index 2a5a6452f7..c368ecb842 100644
--- a/io.c
+++ b/io.c
@@ -3459,7 +3459,7 @@ fptr_finalize(rb_io_t *fptr, int noraise)
 {
     VALUE err = Qnil;
     if (fptr->writeconv) {
-	if (fptr->write_lock) {
+	if (fptr->write_lock && !noraise) {
             struct finish_writeconv_arg arg;
             arg.fptr = fptr;
             arg.noalloc = noraise;
@@ -3470,8 +3470,14 @@ fptr_finalize(rb_io_t *fptr, int noraise)
 	}
     }
     if (fptr->wbuf_len) {
-        if (io_fflush(fptr) < 0 && NIL_P(err))
-            err = noraise ? Qtrue : INT2NUM(errno);
+	if (noraise) {
+	    if ((int)io_flush_buffer_sync(fptr) < 0 && NIL_P(err))
+		err = Qtrue;
+	}
+	else {
+	    if (io_fflush(fptr) < 0 && NIL_P(err))
+		err = INT2NUM(errno);
+	}
     }
     if (IS_PREP_STDIO(fptr) || fptr->fd <= 2) {
         goto skip_fd_close;
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 1cfcba181a..0d89b58b59 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1625,4 +1625,33 @@ End
       end
     end.each {|th| th.join}
   end
+
+  def test_flush_in_finalizer1
+    require 'tempfile'
+    bug3910 = '[ruby-dev:42341]'
+    path = Tempfile.new("bug3910").path
+    fds = []
+    assert_nothing_raised(TypeError, bug3910) do
+      500.times {
+        f = File.open(path, "w")
+        fds << f.fileno
+        f.print "hoge"
+      }
+    end
+  ensure
+    fds.each {|fd| IO.for_fd(fd).close rescue next}
+  end
+
+  def test_flush_in_finalizer2
+    require 'tempfile'
+    bug3910 = '[ruby-dev:42341]'
+    path = Tempfile.new("bug3910").path
+    1.times do
+      io = open(path,"w")
+      io.print "hoge"
+    end
+    assert_nothing_raised(TypeError, bug3910) do
+      GC.start
+    end
+  end
 end