diff --git a/ChangeLog b/ChangeLog
index 114655051b..0c9eb0c425 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Jun 30 11:36:04 2014  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
+
+	* file.c: [DOC] document File.join returns a string.
+	  Contributed by @dapplebeforedawn. [fix GH-646]
+
 Sat Jun 28 22:57:01 2014  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* ext/pathname/pathname.c (path_birthtime): Windows support.
diff --git a/file.c b/file.c
index a2d6681700..196efbbba3 100644
--- a/file.c
+++ b/file.c
@@ -4291,7 +4291,7 @@ rb_file_join(VALUE ary, VALUE sep)
 
 /*
  *  call-seq:
- *     File.join(string, ...)  ->  path
+ *     File.join(string, ...)  ->  string
  *
  *  Returns a new string formed by joining the strings using
  *  <code>File::SEPARATOR</code>.