diff --git a/ChangeLog b/ChangeLog
index 5788cbe039..4218952d77 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat May 29 23:30:33 2010  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* string.c (str_replace_shared): change embedded state atomically.
+	  [ruby-core:29953] [ruby-dev:41456]
+
 Sat May 29 12:56:09 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* encoding.c (rb_filesystem_encindex): avoid infinite require
diff --git a/string.c b/string.c
index f2f49abaff..ae4289380f 100644
--- a/string.c
+++ b/string.c
@@ -613,8 +613,8 @@ str_replace_shared(VALUE str2, VALUE str)
 	STR_SET_EMBED_LEN(str2, RSTRING_LEN(str));
     }
     else {
-	FL_SET(str2, STR_NOEMBED);
 	str = rb_str_new_frozen(str);
+	FL_SET(str2, STR_NOEMBED);
 	RSTRING(str2)->as.heap.len = RSTRING_LEN(str);
 	RSTRING(str2)->as.heap.ptr = RSTRING_PTR(str);
 	RSTRING(str2)->as.heap.aux.shared = str;