diff --git a/core/modules/field/field.post_update.php b/core/modules/field/field.post_update.php
index 4752854..0341bd3 100644
--- a/core/modules/field/field.post_update.php
+++ b/core/modules/field/field.post_update.php
@@ -58,7 +58,7 @@ function field_post_update_email_widget_size_setting() {
   foreach (EntityFormDisplay::loadMultiple() as $entity_form_display) {
     $changed = FALSE;
     foreach ($entity_form_display->getComponents() as $name => $options) {
-      if ($options['type'] == 'email_default') {
+      if (isset($options['type']) && $options['type'] === 'email_default') {
         $options['settings']['size'] = '60';
         $entity_form_display->setComponent($name, $options);
         $changed = TRUE;
diff --git a/core/modules/field/src/Tests/Update/EmailWidgetSizeSettingUpdateTest.php b/core/modules/field/src/Tests/Update/EmailWidgetSizeSettingUpdateTest.php
new file mode 100644
index 0000000..0a4a80a
--- /dev/null
+++ b/core/modules/field/src/Tests/Update/EmailWidgetSizeSettingUpdateTest.php
@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\field\Tests\Update\EntityReferenceHandlerSettingUpdateTest.
+ */
+
+namespace Drupal\field\Tests\Update;
+
+use Drupal\system\Tests\Update\UpdatePathTestBase;
+
+/**
+ * Tests the update for the 'size' setting of the 'email_default' field widget.
+ *
+ * @group field
+ */
+class EmailWidgetSizeSettingUpdateTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../../system/tests/fixtures/update/drupal-8.bare.standard.php.gz',
+      __DIR__ . '/../../../tests/fixtures/update/drupal-8.email_widget_size_setting-2578741.php',
+    ];
+  }
+
+  /**
+   * Tests field_post_update_email_widget_size_setting().
+   *
+   * @see field_post_update_email_widget_size_setting()
+   */
+  public function testFieldPostUpdateEmailWidgetSizeSetting() {
+    $configFactory = $this->container->get('config.factory');
+
+    // Load the 'node.article.default' entity form display and check that the
+    // widget for 'field_email' does not have a 'size' setting.
+    /** @var \Drupal\Core\Config\Config */
+    $config = $configFactory->get('core.entity_form_display.node.article.default');
+    $settings = $config->get('content.field_email_2578741.settings');
+    $this->assertTrue(!isset($settings['size']), 'The size setting does not exist prior to running the update functions.');
+
+    // Run updates.
+    $this->runUpdates();
+
+    // Reload the config and check that the 'size' setting has been populated.
+    $config = $configFactory->get('core.entity_form_display.node.article.default');
+    $settings = $config->get('content.field_email_2578741.settings');
+    $this->assertEqual($settings['size'], 60, 'The size setting exists and it has the correct default value.');
+  }
+
+}
diff --git a/core/modules/field/tests/fixtures/update/drupal-8.email_widget_size_setting-2578741.php b/core/modules/field/tests/fixtures/update/drupal-8.email_widget_size_setting-2578741.php
new file mode 100644
index 0000000..ca762bc
--- /dev/null
+++ b/core/modules/field/tests/fixtures/update/drupal-8.email_widget_size_setting-2578741.php
@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * @file
+ * Contains SQL necessary to add a new component for an email field/widget to
+ * the 'node.article.default' entity form display.
+ */
+
+use Drupal\Core\Database\Database;
+
+$connection = Database::getConnection();
+
+$config = $connection->select('config', 'c')
+  ->fields('c')
+  ->condition('collection', '')
+  ->condition('name', 'core.entity_form_display.node.article.default')
+  ->execute()
+  ->fetchAssoc();
+
+$data = unserialize($config['data']);
+
+// Manually add a new component that simulates an email field using the default
+// email widget.
+$data['content']['field_email_2578741'] = [
+  'weight' => 20,
+  'settings' => [
+    'placeholder' => '',
+  ],
+  'third_party_settings' => [],
+  'type' => 'email_default',
+];
+
+$connection->update('config')
+  ->fields(['data' => serialize($data)])
+  ->condition('collection', '')
+  ->condition('name', 'core.entity_form_display.node.article.default')
+  ->execute();