diff --git a/lib/events.js b/lib/events.js
index d0bcc3b79a6..280ef979ab4 100644
--- a/lib/events.js
+++ b/lib/events.js
@@ -288,11 +288,14 @@ EventEmitter.prototype.removeAllListeners = function(type) {
 };
 
 EventEmitter.prototype.listeners = function(type) {
-  if (!this._events || !this._events[type]) return [];
-  if (!isArray(this._events[type])) {
+  if (typeof type !== 'string')
+    throw TypeError('event type must be a string');
+
+  if (!this._events || !this._events[type])
+    return [];
+  if (typeof this._events[type] === 'function')
     return [this._events[type]];
-  }
-  return this._events[type].slice(0);
+  return this._events[type].slice();
 };
 
 EventEmitter.listenerCount = function(emitter, type) {