diff -u b/core/modules/comment/lib/Drupal/comment/Entity/Comment.php b/core/modules/comment/lib/Drupal/comment/Entity/Comment.php
--- b/core/modules/comment/lib/Drupal/comment/Entity/Comment.php
+++ b/core/modules/comment/lib/Drupal/comment/Entity/Comment.php
@@ -472,7 +472,7 @@
    * {@inheritdoc}
    */
   public function getAuthorId() {
-    return $this->get('uid')->value;
+    return $this->get('uid')->target_id;
   }
 
   /**
diff -u b/core/modules/file/lib/Drupal/file/Entity/File.php b/core/modules/file/lib/Drupal/file/Entity/File.php
--- b/core/modules/file/lib/Drupal/file/Entity/File.php
+++ b/core/modules/file/lib/Drupal/file/Entity/File.php
@@ -128,7 +128,7 @@
    * {@inheritdoc}
    */
   public function getAuthorId() {
-    return $this->get('uid')->value;
+    return $this->get('uid')->target_id;
   }
 
   /**
diff -u b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php
--- b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php
+++ b/core/modules/system/tests/modules/entity_test/lib/Drupal/entity_test/Entity/EntityTest.php
@@ -160,7 +160,7 @@
    * {@inheritdoc}
    */
   public function getAuthorId() {
-    return $this->get('user_id')->value;
+    return $this->get('user_id')->target_id;
   }
 
   /**