diff --git a/lib/proto.js b/lib/proto.js
index 7331887a..5b775308 100644
--- a/lib/proto.js
+++ b/lib/proto.js
@@ -101,7 +101,7 @@ function extendMeta(a, b, prepend) {
       a[p] = val;
     else if (val instanceof Array && a[p] instanceof Array)
       a[p] = [].concat(prepend ? val : a[p]).concat(prepend ? a[p] : val);
-    else if (typeof val == 'object' && typeof a[p] == 'object')
+    else if (typeof val == 'object' && val !== null && typeof a[p] == 'object')
       a[p] = extend(extend({}, a[p]), val, prepend);
     else if (!prepend)
       a[p] = val;