diff --git a/index.js b/index.js
index dfaa0fe..2a41cd8 100644
--- a/index.js
+++ b/index.js
@@ -42,12 +42,13 @@ function perform(action /* , args..., performFn, callback*/) {
   if (typeof action !== 'string') throw new Error('event must be a string');
   var callback = arguments[arguments.length - 1];
   var performFn = arguments[arguments.length - 2];
+  if (typeof callback !== 'function') {
+    throw new Error('last argument must be a function');
+  }
+
+  // Allow callback to be omitted by using last arg as performFn
   var slice = -2;
   if (typeof performFn !== 'function') {
-    if (typeof callback !== 'function') {
-      throw new Error('performFn and callback must be a function');
-    }
-
     performFn = callback;
     callback = null;
     slice = -1;
diff --git a/test/no-functions.js b/test/no-functions.js
index f319fdd..84eca7d 100644
--- a/test/no-functions.js
+++ b/test/no-functions.js
@@ -5,13 +5,20 @@ var Understudy = require('../').Understudy;
 var actor = new Understudy();
 
 actor.before('no-functions', function () {
-  assert.equal(true, false);
+  throw new Error('before shouldn\'t be reached');
 });
 
 actor.after('no-functions', function () {
-  assert.equal(true, false);
+  throw new Error('after shouldn\'t be reached');
 });
 
 assert.throws(function () {
-  actor.perform('no-functions', 'NO', 'AFTER');
-});
+  actor.perform('no-functions', 'INVALID ACTION', 'INVALID CALLBACK');
+}, /last argument must be a function/);
+
+assert.throws(function () {
+  function action () {
+  	throw new Error('action shouldn\'t be reached');
+  }
+  actor.perform('no-functions', action, 'INVALID CALLBACK');
+}, /last argument must be a function/);