diff --git a/resources/assets/js/views/common/documents.js b/resources/assets/js/views/common/documents.js
index 65d6cde05..339a198b5 100644
--- a/resources/assets/js/views/common/documents.js
+++ b/resources/assets/js/views/common/documents.js
@@ -816,6 +816,10 @@ const app = new Vue({
 
     watch: {
         'form.discount': function (newVal, oldVal) {
+            if (typeof newVal !== 'string') {
+                return;
+            }
+
             if (newVal != '' && newVal.search('^[-+]?([0-9]|[1-9][0-9]|100)*\.?[0-9]+$') !== 0) {
                 this.form.discount = oldVal;
                 this.form.discount = this.form.discount ? this.form.discount.replace(',', '.') : '';