diff --git a/ChangeLog b/ChangeLog
index 6cadd20b38..58a8ea5433 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Dec 26 17:31:08 2007  Tanaka Akira  <akr@fsij.org>
+
+	* io.c (io_fflush): check closed fptr after rb_write_internal to avoid
+	  SEGV on MacOS X.
+
 Wed Dec 26 16:10:17 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* string.c (Init_String): defines chars method.
diff --git a/io.c b/io.c
index 7c5ee6f205..b5641b2e78 100644
--- a/io.c
+++ b/io.c
@@ -534,7 +534,8 @@ io_fflush(rb_io_t *fptr)
         l = PIPE_BUF;
     }
     r = rb_write_internal(fptr->fd, fptr->wbuf+fptr->wbuf_off, l);
-    /* xxx: signal handler may modify wbuf */
+    /* xxx: other threads may modify wbuf */
+    rb_io_check_closed(fptr);
     if (r == fptr->wbuf_len) {
         fptr->wbuf_off = 0;
         fptr->wbuf_len = 0;