diff --git a/Library/Homebrew/formula_pin.rb b/Library/Homebrew/formula_pin.rb
index 7ecad9d7b2..c9a195fdd9 100644
--- a/Library/Homebrew/formula_pin.rb
+++ b/Library/Homebrew/formula_pin.rb
@@ -18,7 +18,7 @@ class FormulaPin
   end
 
   def pin
-    pin_at(@f.rack.subdirs.map { |d| Keg.new(d).version }.max)
+    pin_at(@f.installed_kegs.map { |keg| keg.version }.max)
   end
 
   def unpin
@@ -31,7 +31,7 @@ class FormulaPin
   end
 
   def pinnable?
-    @f.rack.exist? && @f.rack.subdirs.length > 0
+    @f.installed_prefixes.any?
   end
 
   def pinned_version