diff --git a/lib/context.js b/lib/context.js
index 0511558..fc1d6e5 100644
--- a/lib/context.js
+++ b/lib/context.js
@@ -87,7 +87,7 @@ var proto = module.exports = {
     // don't do anything if there is no error.
     // this allows you to pass `this.onerror`
     // to node-style callbacks.
-    if (undefined == err) return;
+    if (null == err) return;
 
     assert(err instanceof Error, 'non-error thrown: ' + err);