diff --git a/ChangeLog b/ChangeLog
index e3f6bc36e9..ac7496efa8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Jun 29 21:11:15 2010  Masaya Tarui  <tarui@ruby-lnag.org>
+
+	* ext/stringio/stringio.c (strio_write): add RB_GC_GUARD.
+
+
 Tue Jun 29 19:39:59 2010  Masaki Suketa <masaki.suketa@nifty.ne.jp>
 
 	* test/win32ole/test_win32ole_method.rb (is_ruby64): check
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index a554e7187a..c93ba10466 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1107,6 +1107,7 @@ strio_write(VALUE self, VALUE str)
     long len, olen;
     rb_encoding *enc, *enc2;
 
+    RB_GC_GUARD(str);
     if (TYPE(str) != T_STRING)
 	str = rb_obj_as_string(str);
     enc = rb_enc_get(ptr->string);