diff --git a/ChangeLog b/ChangeLog
index c7fd673de1..064f4e6dad 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Apr 21 19:12:20 2014  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* string.c (rb_str_coderange_scan_restartable): coderange is always
+	  ENC_CODERANGE_VALID if the string is ASCII-8BIT and already has a non
+	  ASCII character.
+
 Mon Apr 21 19:02:44 2014  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* string.c (coderange_scan): remove useless condtion `p < e` after
diff --git a/string.c b/string.c
index 79ac7aeecc..c589c80d2e 100644
--- a/string.c
+++ b/string.c
@@ -304,7 +304,7 @@ coderange_scan(const char *p, long len, rb_encoding *enc)
 {
     const char *e = p + len;
 
-    if (rb_enc_to_index(enc) == 0) {
+    if (rb_enc_to_index(enc) == rb_ascii8bit_encindex()) {
         /* enc is ASCII-8BIT.  ASCII-8BIT string never be broken. */
         p = search_nonascii(p, e);
         return p ? ENC_CODERANGE_VALID : ENC_CODERANGE_7BIT;
@@ -340,10 +340,11 @@ rb_str_coderange_scan_restartable(const char *s, const char *e, rb_encoding *enc
     if (*cr == ENC_CODERANGE_BROKEN)
 	return e - s;
 
-    if (rb_enc_to_index(enc) == 0) {
+    if (rb_enc_to_index(enc) == rb_ascii8bit_encindex()) {
 	/* enc is ASCII-8BIT.  ASCII-8BIT string never be broken. */
+	if (*cr == ENC_CODERANGE_VALID) return e - s;
 	p = search_nonascii(p, e);
-	*cr = (!p && *cr != ENC_CODERANGE_VALID) ? ENC_CODERANGE_7BIT : ENC_CODERANGE_VALID;
+        *cr = p ? ENC_CODERANGE_VALID : ENC_CODERANGE_7BIT;
 	return e - s;
     }
     else if (rb_enc_asciicompat(enc)) {