diff --git a/partner-simplepay.js b/partner-simplepay.js
index 3b7000f..2f3f220 100644
--- a/partner-simplepay.js
+++ b/partner-simplepay.js
@@ -175,7 +175,7 @@ function _responseBodyHandler(responseBody, task) {
     const diag = _getPropertyFromObjectSafe(response.data, 'diag');
     let balance = _getPropertyFromObjectSafe(response.data, 'balance');
 
-    if (balance && aaa.updateBalance) {
+    if ((typeof balance === 'string') && balance && aaa.updateBalance) {
         balance = balance.replace(/\D/g, '');
         if (balance) {
             aaa.updateBalance(balance);