diff --git a/ChangeLog b/ChangeLog
index 71883d54e6..9eb3a87b9d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Tue Feb 16 02:49:41 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* tool/rbinstall.rb (without_destdir): compare with the destdir
+	  after stripping a drive letter, on dosish platforms.
+	  pointed out by @DavidEGrayson.
+	  https://github.com/ruby/ruby/commit/d0cf23b#commitcomment-16100407
+
 Mon Feb 15 15:44:09 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* parse.y (parse_ident): allow keyword arguments just after a
diff --git a/tool/rbinstall.rb b/tool/rbinstall.rb
index 4614c3538a..1cca55d919 100755
--- a/tool/rbinstall.rb
+++ b/tool/rbinstall.rb
@@ -281,9 +281,9 @@ def with_destdir(dir)
 end
 
 def without_destdir(dir)
-  return dir if !$destdir or $destdir.empty? or !dir.start_with?($destdir)
+  return dir if !$destdir or $destdir.empty?
   dir = dir.sub(/\A\w:/, '') if File::PATH_SEPARATOR == ';'
-  dir[$destdir.size..-1]
+  dir.start_with?($destdir) ? dir[$destdir.size..-1] : dir
 end
 
 def prepare(mesg, basedir, subdirs=nil)