diff --git a/ChangeLog b/ChangeLog
index 23dab6aa0b..0c34e27ebe 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jun  8 04:52:40 2014  Jun Hiroe  <Jun.Hiroe@gmail.com>
+
+	* string.c (rb_str_slice_bang): [DOC] update return value against
+	  a fixnum, which has changed because of M17N.  [fix GH-631]
+
 Sat Jun  7 22:13:42 2014  Benoit Daloze  <eregontp@gmail.com>
 
 	* numeric.c (do_coerce): Add a warning when an exception is raised
diff --git a/string.c b/string.c
index 15e6bcd623..0e589243af 100644
--- a/string.c
+++ b/string.c
@@ -3782,7 +3782,7 @@ rb_str_insert(VALUE str, VALUE idx, VALUE str2)
 
 /*
  *  call-seq:
- *     str.slice!(fixnum)           -> fixnum or nil
+ *     str.slice!(fixnum)           -> new_str or nil
  *     str.slice!(fixnum, fixnum)   -> new_str or nil
  *     str.slice!(range)            -> new_str or nil
  *     str.slice!(regexp)           -> new_str or nil