diff --git a/app/code/Magento/Customer/Model/Plugin/CustomerFlushFormKey.php b/app/code/Magento/Customer/Model/Plugin/CustomerFlushFormKey.php
index b7b462b3cc317..2d000ccfb4b93 100644
--- a/app/code/Magento/Customer/Model/Plugin/CustomerFlushFormKey.php
+++ b/app/code/Magento/Customer/Model/Plugin/CustomerFlushFormKey.php
@@ -45,7 +45,7 @@ public function aroundExecute(FlushFormKey $subject, callable $proceed, ...$args
         $currentFormKey = $this->dataFormKey->getFormKey();
         $proceed(...$args);
         $beforeParams = $this->session->getBeforeRequestParams();
-        if ($beforeParams['form_key'] == $currentFormKey) {
+        if (isset($beforeParams['form_key']) && $beforeParams['form_key'] === $currentFormKey) {
             $beforeParams['form_key'] = $this->dataFormKey->getFormKey();
             $this->session->setBeforeRequestParams($beforeParams);
         }