diff --git a/Library/Homebrew/extend/ARGV.rb b/Library/Homebrew/extend/ARGV.rb
index c217ed8a51..f2f959f221 100644
--- a/Library/Homebrew/extend/ARGV.rb
+++ b/Library/Homebrew/extend/ARGV.rb
@@ -65,6 +65,8 @@ module HomebrewArgvExtension
     require "keg"
     require "formula"
     @kegs ||= downcased_unique_named.collect do |name|
+      raise UsageError if name.empty?
+
       rack = Formulary.to_rack(name.downcase)
 
       dirs = rack.directory? ? rack.subdirs : []