diff --git a/ChangeLog b/ChangeLog
index 4ce8b085f0..7d3508490f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Feb 16 19:04:17 2008  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* string.c (str_strlen): revert r15507. [ruby-dev:33810]
+
 Sat Feb 16 18:25:14 2008  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* string.c (str_strlen): little more optimize.
diff --git a/string.c b/string.c
index e6670d31ba..341bfd7463 100644
--- a/string.c
+++ b/string.c
@@ -667,9 +667,6 @@ str_strlen(VALUE str, rb_encoding *enc)
     if (len < 0) {
 	rb_raise(rb_eArgError, "invalid mbstring sequence");
     }
-    if (ENC_CODERANGE(str) != ENC_CODERANGE_VALID && enc == STR_ENC_GET(str)) {
-	ENC_CODERANGE_SET(str, ENC_CODERANGE_VALID);
-    }
     return len;
 }