diff --git a/lib/cli.ex b/lib/cli.ex
index bd02577..fbad44f 100644
--- a/lib/cli.ex
+++ b/lib/cli.ex
@@ -4,21 +4,16 @@ defmodule Onigumo.CLI do
   }
 
   def main(argv) do
-    case OptionParser.parse(
-           argv,
-           aliases: [C: :working_dir],
-           strict: [working_dir: :string]
-         ) do
-      {switches, [component], []} ->
-        with {:ok, module} <- Map.fetch(@components, String.to_atom(component)) do
-          working_dir = Keyword.get(switches, :working_dir, File.cwd!())
-          module.main(working_dir)
-        else
-          :error -> usage_message()
-        end
+    parsed = OptionParser.parse(argv, aliases: [C: :working_dir], strict: [working_dir: :string])
 
-      _ ->
-        usage_message()
+    with {switches, [component], []} <- parsed,
+         {:ok, module} <- Map.fetch(@components, String.to_atom(component)) do
+      working_dir = Keyword.get(switches, :working_dir, File.cwd!())
+      module.main(working_dir)
+    else
+      {_, _, [_ | _]} -> usage_message()
+      {_, argv, _} when length(argv) != 1 -> usage_message()
+      :error -> usage_message()
     end
   end