diff --git a/src/Webpay/WebpayPlus/MallTransaction.php b/src/Webpay/WebpayPlus/MallTransaction.php
index 303dd44c..6874687c 100644
--- a/src/Webpay/WebpayPlus/MallTransaction.php
+++ b/src/Webpay/WebpayPlus/MallTransaction.php
@@ -77,6 +77,13 @@ public function create($buyOrder, $sessionId, $returnUrl, $details)
      */
     public function commit($token)
     {
+        if (!is_string($token)) {
+            throw new InvalidArgumentException('Token parameter given is not string.');
+        }
+        if (!isset($token) || trim($token) === '') {
+            throw new InvalidArgumentException('Token parameter given is empty.');
+        }
+
         try {
             $response = $this->sendRequest(
                 'PUT',
diff --git a/src/Webpay/WebpayPlus/Transaction.php b/src/Webpay/WebpayPlus/Transaction.php
index e8b8238e..1d5ca031 100644
--- a/src/Webpay/WebpayPlus/Transaction.php
+++ b/src/Webpay/WebpayPlus/Transaction.php
@@ -70,6 +70,13 @@ public function create($buyOrder, $sessionId, $amount, $returnUrl)
      */
     public function commit($token)
     {
+        if (!is_string($token)) {
+            throw new InvalidArgumentException('Token parameter given is not string.');
+        }
+        if (!isset($token) || trim($token) === '') {
+            throw new InvalidArgumentException('Token parameter given is empty.');
+        }
+
         try {
             $response = $this->sendRequest(
                 'PUT',