diff --git a/ChangeLog b/ChangeLog
index 480b809a35..2e3b17a6dd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Feb  7 16:33:51 2008  Tanaka Akira  <akr@fsij.org>
+
+	* io.c (io_reopen): don't change access mode for stdin, stdout and
+	  stderr.  [ruby-core:15360]
+
 Thu Feb  7 16:33:48 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* string.c (str_replace_shared): replaces string with sharing.
diff --git a/bootstraptest/test_io.rb b/bootstraptest/test_io.rb
index 55b7ce01cb..a5d54afc5b 100644
--- a/bootstraptest/test_io.rb
+++ b/bootstraptest/test_io.rb
@@ -36,3 +36,19 @@ assert_finish 1, %q{
   }
   r.gets("abab")
 }
+
+assert_equal 'ok', %q{
+  require 'tmpdir'
+  begin
+    tmpname = "#{Dir.tmpdir}/ruby-btest-#{$$}-#{rand(0x100000000).to_s(36)}"
+    rw = File.open(tmpname, File::RDWR|File::CREAT|File::EXCL)
+  rescue Errno::EEXIST
+    retry
+  end
+  save = STDIN.dup
+  STDIN.reopen(rw)
+  STDIN.reopen(save)
+  rw.close
+  File.unlink(tmpname)
+  :ok
+}
diff --git a/io.c b/io.c
index b20b0fd4a9..44d9b3728e 100644
--- a/io.c
+++ b/io.c
@@ -4132,7 +4132,13 @@ io_reopen(VALUE io, VALUE nfile)
     }
 
     /* copy rb_io_t structure */
-    fptr->mode = orig->mode | (fptr->mode & FMODE_PREP);
+    if (fptr->mode & FMODE_PREP) {
+        int mask = FMODE_PREP|FMODE_READWRITE;
+        fptr->mode = (orig->mode & ~mask)|(fptr->mode & mask);
+    }
+    else {
+        fptr->mode = orig->mode;
+    }
     fptr->pid = orig->pid;
     fptr->lineno = orig->lineno;
     if (fptr->path) free(fptr->path);