diff --git a/model/index.js b/model/index.js
index e5620825..63a3b7e1 100644
--- a/model/index.js
+++ b/model/index.js
@@ -2,6 +2,7 @@ const deepmerge = require('deepmerge');
 
 module.exports = {
     extend: (base, target, options = {}) => {
+        base = deepmerge({}, base);
         const fieldsToMerge = (target.fields || []).map(df => df.fieldname);
         const fieldsToRemove = options.skipFields || [];