diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php
index 9f2096f26eb08507dbc2415e330f75d2451949b7..9c53665ab55831e36f112dabfdee6993c806d5be 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/ChangedItem.php
@@ -13,7 +13,7 @@
  *   label = @Translation("Last changed"),
  *   description = @Translation("An entity field containing a UNIX timestamp of when the entity has been last updated."),
  *   no_ui = TRUE,
- *   default_widget = "datetime_default",
+ *   default_widget = "datetime_timestamp",
  *   default_formatter = "timestamp",
  *   list_class = "\Drupal\Core\Field\ChangedFieldItemList"
  * )
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/CreatedItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/CreatedItem.php
index 228c8e6bbac15c0228cf72443a6d02c020b0eebd..da2e2a74506b31ae2f3e9b0f380c632776c17619 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/CreatedItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/CreatedItem.php
@@ -10,7 +10,7 @@
  *   label = @Translation("Created"),
  *   description = @Translation("An entity field containing a UNIX timestamp of when the entity has been created."),
  *   no_ui = TRUE,
- *   default_widget = "datetime_default",
+ *   default_widget = "datetime_timestamp",
  *   default_formatter = "timestamp"
  * )
  */
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/TimestampItem.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/TimestampItem.php
index f48e4f01cac608a4c81416694c4fa850f086ecaf..8c3ffd2119243ae23d19c063e64be856943d32a1 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/TimestampItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/TimestampItem.php
@@ -13,7 +13,7 @@
  *   id = "timestamp",
  *   label = @Translation("Timestamp"),
  *   description = @Translation("An entity field containing a UNIX timestamp value."),
- *   default_widget = "datetime_default",
+ *   default_widget = "datetime_timestamp",
  *   default_formatter = "timestamp",
  *   constraints = {
  *     "ComplexData" = {
diff --git a/core/modules/system/system.post_update.php b/core/modules/system/system.post_update.php
index 01f304b2083c966bf29cc81daf5b405188f1638a..e123f91fc90d51dc0a958ad99154416454a5b271 100644
--- a/core/modules/system/system.post_update.php
+++ b/core/modules/system/system.post_update.php
@@ -65,3 +65,21 @@ function system_post_update_add_region_to_entity_displays() {
 function system_post_update_hashes_clear_cache() {
   // Empty post-update hook.
 }
+
+/**
+ * @addtogroup updates-8.3.x
+ * @{
+ */
+
+/**
+ * Force plugin definitions to be cleared.
+ *
+ * @see https://www.drupal.org/node/2802663
+ */
+function system_post_update_timestamp_plugins() {
+  // Empty post-update hook.
+}
+
+/**
+ * @} End of "addtogroup uupdates-8.3.x".
+ */
diff --git a/core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php b/core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..8faf8c6c915e047554b1c12a145cb15a850dec9f
--- /dev/null
+++ b/core/tests/Drupal/FunctionalTests/Datetime/TimestampTest.php
@@ -0,0 +1,149 @@
+<?php
+
+namespace Drupal\FunctionalTests\Datetime;
+
+use Drupal\Core\Datetime\DrupalDateTime;
+use Drupal\Core\Datetime\Entity\DateFormat;
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the functionality of Timestamp core field UI.
+ *
+ * @group field
+ */
+class TimestampTest extends BrowserTestBase {
+
+  /**
+   * An array of display options to pass to entity_get_display().
+   *
+   * @var array
+   */
+  protected $displayOptions;
+
+  /**
+   * A field storage to use in this test class.
+   *
+   * @var \Drupal\field\Entity\FieldStorageConfig
+   */
+  protected $fieldStorage;
+
+  /**
+   * The field used in this test class.
+   *
+   * @var \Drupal\field\Entity\FieldConfig
+   */
+  protected $field;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['node', 'entity_test', 'field_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $web_user = $this->drupalCreateUser([
+      'access content',
+      'view test entity',
+      'administer entity_test content',
+      'administer entity_test form display',
+      'administer content types',
+      'administer node fields',
+    ]);
+
+    $this->drupalLogin($web_user);
+    $field_name = 'field_timestamp';
+    $type = 'timestamp';
+    $widget_type = 'datetime_timestamp';
+    $formatter_type = 'timestamp';
+
+    $this->fieldStorage = FieldStorageConfig::create([
+      'field_name' => $field_name,
+      'entity_type' => 'entity_test',
+      'type' => $type,
+    ]);
+    $this->fieldStorage->save();
+    $this->field = FieldConfig::create([
+      'field_storage' => $this->fieldStorage,
+      'bundle' => 'entity_test',
+      'required' => TRUE,
+    ]);
+    $this->field->save();
+
+    EntityFormDisplay::load('entity_test.entity_test.default')
+      ->setComponent($field_name, ['type' => $widget_type])
+      ->save();
+
+    $this->displayOptions = [
+      'type' => $formatter_type,
+      'label' => 'hidden',
+    ];
+
+    EntityViewDisplay::create([
+      'targetEntityType' => $this->field->getTargetEntityTypeId(),
+      'bundle' => $this->field->getTargetBundle(),
+      'mode' => 'full',
+      'status' => TRUE,
+    ])->setComponent($field_name, $this->displayOptions)
+      ->save();
+  }
+
+  /**
+   * Tests the "datetime_timestamp" widget.
+   */
+  public function testWidget() {
+    // Build up a date in the UTC timezone.
+    $value = '2012-12-31 00:00:00';
+    $date = new DrupalDateTime($value, 'UTC');
+
+    // Update the timezone to the system default.
+    $date->setTimezone(timezone_open(drupal_get_user_timezone()));
+
+    // Display creation form.
+    $this->drupalGet('entity_test/add');
+
+    // Make sure the "datetime_timestamp" widget is on the page.
+    $fields = $this->xpath('//div[contains(@class, "field--widget-datetime-timestamp") and @id="edit-field-timestamp-wrapper"]');
+    $this->assertEquals(1, count($fields));
+
+    // Look for the widget elements and make sure they are empty.
+    $this->assertSession()->fieldExists('field_timestamp[0][value][date]');
+    $this->assertSession()->fieldValueEquals('field_timestamp[0][value][date]', '');
+    $this->assertSession()->fieldExists('field_timestamp[0][value][time]');
+    $this->assertSession()->fieldValueEquals('field_timestamp[0][value][time]', '');
+
+    // Submit the date.
+    $date_format = DateFormat::load('html_date')->getPattern();
+    $time_format = DateFormat::load('html_time')->getPattern();
+
+    $edit = [
+      'field_timestamp[0][value][date]' => $date->format($date_format),
+      'field_timestamp[0][value][time]' => $date->format($time_format),
+    ];
+    $this->drupalPostForm(NULL, $edit, 'Save');
+
+    // Make sure the submitted date is set as the default in the widget.
+    $this->assertSession()->fieldExists('field_timestamp[0][value][date]');
+    $this->assertSession()->fieldValueEquals('field_timestamp[0][value][date]', $date->format($date_format));
+    $this->assertSession()->fieldExists('field_timestamp[0][value][time]');
+    $this->assertSession()->fieldValueEquals('field_timestamp[0][value][time]', $date->format($time_format));
+
+    // Make sure the entity was saved.
+    preg_match('|entity_test/manage/(\d+)|', $this->getSession()->getCurrentUrl(), $match);
+    $id = $match[1];
+    $this->assertSession()->pageTextContains(sprintf('entity_test %s has been created.', $id));
+
+    // Make sure the timestamp is output properly with the default formatter.
+    $medium = DateFormat::load('medium')->getPattern();
+    $this->drupalGet('entity_test/' . $id);
+    $this->assertSession()->pageTextContains($date->format($medium));
+  }
+
+}