diff --git a/lib/functions.js b/lib/functions.js
index <HASH>..<HASH> 100644
--- a/lib/functions.js
+++ b/lib/functions.js
@@ -25,7 +25,7 @@ internals.pick = function () {
 internals.include = function (o) {
   if (!o || !(o instanceof Object))
     throw new Error('Pick must have params (arguments)');
-  return _.merge(this._joi, o);
+  return _.merge({}, this._joi, o);
 };
 
 internals.withRequired = function () {
[hotfix] change include function to don't permanently change _joi object