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 8f0c249..1c5e49b 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/TimestampItem.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldType/TimestampItem.php
@@ -24,21 +24,12 @@
 class TimestampItem extends FieldItemBase {
 
   /**
-   * Definitions of the contained properties.
-   *
-   * @var array
-   */
-  public static $propertyDefinitions;
-
-  /**
    * {@inheritdoc}
    */
-  public function getPropertyDefinitions() {
-    if (!isset(static::$propertyDefinitions)) {
-      static::$propertyDefinitions['value'] = DataDefinition::create('timestamp')
-        ->setLabel(t('Timestamp value'));
-    }
-    return static::$propertyDefinitions;
+  public static function propertyDefinitions(FieldDefinitionInterface $field_definition) {
+    $properties['value'] = DataDefinition::create('timestamp')
+      ->setLabel(t('Timestamp value'));
+    return $properties;
   }
 
   /**