diff --git a/Library/Homebrew/requirements/ruby_requirement.rb b/Library/Homebrew/requirements/ruby_requirement.rb
index 817cf3e327..f03399078f 100644
--- a/Library/Homebrew/requirements/ruby_requirement.rb
+++ b/Library/Homebrew/requirements/ruby_requirement.rb
@@ -40,7 +40,7 @@ class RubyRequirement < Requirement
 
   def rubies
     rubies = which_all("ruby")
-    if ruby_formula.installed?
+    if ruby_formula && ruby_formula.installed?
       rubies.unshift Pathname.new(ruby_formula.bin/"ruby")
     end
     rubies.uniq