diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index e44a4cfb02..bb1d91687b 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -355,6 +355,8 @@ class Formula
   end
 
   def self.installed
+    return [] unless HOMEBREW_CELLAR.directory?
+
     HOMEBREW_CELLAR.children.map do |rack|
       begin
         factory(rack.basename.to_s)