diff --git a/app/code/Magento/Theme/view/frontend/templates/html/header.phtml b/app/code/Magento/Theme/view/frontend/templates/html/header.phtml
index cc3ea276e2230..58548a0ba268a 100644
--- a/app/code/Magento/Theme/view/frontend/templates/html/header.phtml
+++ b/app/code/Magento/Theme/view/frontend/templates/html/header.phtml
@@ -15,7 +15,7 @@ $welcomeMessage = $block->getWelcome();
     case 'welcome': ?>
         <li class="greet welcome" data-bind="scope: 'customer'">
             <!-- ko if: customer().fullname  -->
-            <span data-bind="text: new String('<?= $block->escapeHtml(__('Welcome, %1!', '%1')) ?>').replace('%1', customer().firstname)">
+            <span data-bind="text: new String('<?= $block->escapeHtml(__('Welcome, %1!', '%1')) ?>').replace('%1', customer().fullname)">
             </span>
             <!-- /ko -->
             <!-- ko ifnot: customer().fullname  -->
diff --git a/dev/tests/functional/tests/app/Magento/Checkout/Test/Constraint/AssertCartPerCustomer.php b/dev/tests/functional/tests/app/Magento/Checkout/Test/Constraint/AssertCartPerCustomer.php
index 2442bd8fe1f5f..1aee48ad307ad 100644
--- a/dev/tests/functional/tests/app/Magento/Checkout/Test/Constraint/AssertCartPerCustomer.php
+++ b/dev/tests/functional/tests/app/Magento/Checkout/Test/Constraint/AssertCartPerCustomer.php
@@ -53,7 +53,10 @@ public function processAssert(
                     ['customer' => $customer]
                 )->run();
                 \PHPUnit_Framework_Assert::assertEquals(
-                    sprintf(self::WELCOME_MESSAGE, $customer->getFirstname()),
+                    sprintf(
+                        self::WELCOME_MESSAGE,
+                        $customer->getFirstname() . ' ' . $customer->getLastname()
+                    ),
                     $cmsIndex->getLinksBlock()->getWelcomeText(),
                     'Customer welcome message is wrong.'
                 );