diff --git a/src/mixins/computedFields.js b/src/mixins/computedFields.js
index d438e419d..1939b9df7 100644
--- a/src/mixins/computedFields.js
+++ b/src/mixins/computedFields.js
@@ -1,21 +1,20 @@
+import _ from 'lodash';
 import { Parser } from 'expr-eval';
 
 export default {
   methods: {
     evaluateExpression(expression, type) {
       let value = null;
-      try {
-        const self = this;
 
+      const merged = {};
+      _.merge(merged, this.vdata, this._data);
+
+      try {
         //monitor if variable belongs to data (defined variables) or vdata (external variables)
         //in this way the event is not executed again when the variable is update
-        const data = new Proxy(Object.assign({}, this), {
+        const data = new Proxy(merged, {
           get(data, name) {
-            if (data[name] === undefined) {
-              return self.vdata[name];
-            } else {
-              return data[name];
-            }
+            return data[name];
           },
           set() {
             throw 'You are not allowed to set properties from inside an expression';