diff --git a/ChangeLog b/ChangeLog
index 6f9a67bb0e..261d426c90 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Mon Jul  1 15:03:42 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Mon Jul  1 15:04:20 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/stringio/stringio.c (strio_write): keep coderange of
+	  ptr->string.
 
 	* string.c (rb_enc_cr_str_buf_cat, rb_str_append): consider an empty
 	  string 7bit-clean and should not discard cached coderange of string
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index d15db8b076..57854919cd 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -1182,7 +1182,7 @@ strio_write(VALUE self, VALUE str)
 	ptr->pos = olen;
     }
     if (ptr->pos == olen) {
-	rb_str_cat(ptr->string, RSTRING_PTR(str), len);
+	rb_enc_str_buf_cat(ptr->string, RSTRING_PTR(str), len, enc);
     }
     else {
 	strio_extend(ptr, ptr->pos, len);