diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 2fe4859091..d21fc48b16 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -469,8 +469,9 @@ class Formula
     }
 
     if rack.directory?
-      rack.subdirs.each do |keg|
-        tab = Tab.for_keg keg
+      rack.subdirs.each do |keg_path|
+        keg = Keg.new keg_path
+        tab = Tab.for_keg keg_path
 
         hsh["installed"] << {
           "version" => keg.version.to_s,