diff --git a/Library/Homebrew/cmd/command.rb b/Library/Homebrew/cmd/command.rb
index 6ddd898be3..4790a69524 100644
--- a/Library/Homebrew/cmd/command.rb
+++ b/Library/Homebrew/cmd/command.rb
@@ -1,5 +1,6 @@
 module Homebrew
   def command
+    abort "This command requires a command argument" if ARGV.empty?
     cmd = ARGV.first
     cmd = HOMEBREW_INTERNAL_COMMAND_ALIASES.fetch(cmd, cmd)