diff --git a/core/lib/Drupal/Core/Entity/ContentEntityBase.php b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
index 7c0a458..fe7a53c 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
@@ -163,6 +163,13 @@
   protected $validationRequired = FALSE;
 
   /**
+   * The original revision ID before the new revision was set.
+   *
+   * @var int
+   */
+  protected $originalRevisionId;
+
+  /**
    * {@inheritdoc}
    */
   public function __construct(array $values, $entity_type, $bundle = FALSE, $translations = array()) {
@@ -230,6 +237,11 @@ public function __construct(array $values, $entity_type, $bundle = FALSE, $trans
         }
       }
     }
+    if ($this->getEntityType()->isRevisionable()) {
+      // Store the original revision ID the entity has been loaded with to
+      // keep it safe from changes.
+      $this->originalRevisionId = $this->getRevisionId();
+    }
   }
 
   /**
@@ -284,6 +296,13 @@ public function setNewRevision($value = TRUE) {
   /**
    * {@inheritdoc}
    */
+  public function getOriginalRevisionId() {
+    return $this->originalRevisionId;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function isNewRevision() {
     return $this->newRevision || ($this->getEntityType()->hasKey('revision') && !$this->getRevisionId());
   }
@@ -368,6 +387,19 @@ public function preSaveRevision(EntityStorageInterface $storage, \stdClass $reco
   /**
    * {@inheritdoc}
    */
+  public function postSave(EntityStorageInterface $storage, $update = TRUE) {
+    parent::postSave($storage, $update);
+
+    // If there is an revision ID set it as the original revision ID. Even when
+    // a new revision isn't created the original ID should be set.
+    if ($this->getRevisionId()) {
+      $this->originalRevisionId = $this->getRevisionId();
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function validate() {
     $this->validated = TRUE;
     $violations = $this->getTypedData()->validate();
@@ -996,6 +1028,7 @@ public function createDuplicate() {
     // Check whether the entity type supports revisions and initialize it if so.
     if ($entity_type->isRevisionable()) {
       $duplicate->{$entity_type->getKey('revision')}->value = NULL;
+      $duplicate->originalRevisionId = NULL;
     }
 
     return $duplicate;
diff --git a/core/lib/Drupal/Core/Entity/ContentEntityInterface.php b/core/lib/Drupal/Core/Entity/ContentEntityInterface.php
index 0c3f04b..684aaa7 100644
--- a/core/lib/Drupal/Core/Entity/ContentEntityInterface.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityInterface.php
@@ -53,4 +53,13 @@ public function setRevisionTranslationAffected($affected);
    */
   public function isRevisionTranslationAffected();
 
+  /**
+   * Gets the original revision identifier of the entity.
+   *
+   * @return int
+   *   The original revision identifier of the entity, or NULL if the entity
+   *   does not have a revision identifier.
+   */
+  public function getOriginalRevisionId();
+
 }
diff --git a/core/modules/system/tests/modules/entity_test/entity_test.module b/core/modules/system/tests/modules/entity_test/entity_test.module
index f8f56eb..4192e33 100644
--- a/core/modules/system/tests/modules/entity_test/entity_test.module
+++ b/core/modules/system/tests/modules/entity_test/entity_test.module
@@ -6,6 +6,7 @@
  */
 
 use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Entity\ContentEntityInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
@@ -481,6 +482,10 @@ function entity_test_entity_presave(EntityInterface $entity) {
   if ($entity->getEntityType()->id() == 'entity_view_display') {
     $entity->setThirdPartySetting('entity_test', 'foo', 'bar');
   }
+
+  if ($entity instanceof ContentEntityInterface) {
+    \Drupal::state()->set('entity_test.originalRevisionId', $entity->getOriginalRevisionId());
+  }
 }
 
 /**
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/EntityOriginalRevisionTest.php b/core/tests/Drupal/KernelTests/Core/Entity/EntityOriginalRevisionTest.php
new file mode 100644
index 0000000..cd0fcc6
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntityOriginalRevisionTest.php
@@ -0,0 +1,85 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Entity;
+
+use Drupal\entity_test\Entity\EntityTestMulRev;
+
+/**
+ * Tests the original revision of an entity.
+ *
+ * @group entity
+ */
+class EntityOriginalRevisionTest extends EntityKernelTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = ['system', 'entity_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+
+    $this->installEntitySchema('entity_test_mulrev');
+
+  }
+
+  /**
+   * Test getOriginalRevisionId() returns the correct ID throughout the process.
+   */
+  public function testOriginalRevisionId() {
+    // Create a basic EntityTestMulRev entity and save it.
+    $entity = EntityTestMulRev::create();
+    $entity->save();
+
+    // Load the created entity and create a new revision.
+    $loaded = EntityTestMulRev::load($entity->id());
+    $loaded->setNewRevision(TRUE);
+
+    // Before saving, the original revision ID should be the same as the created
+    // entity, not the same as the loaded entity (which do not have a revision
+    // id yet).
+    $this->assertEquals($entity->getRevisionId(), $loaded->getOriginalRevisionId());
+    $this->assertNotEquals($loaded->getRevisionId(), $loaded->getOriginalRevisionId());
+    $this->assertSame(NULL, $loaded->getRevisionId());
+
+    $loaded->save();
+
+    // In entity_test_entity_presave() the original revision id was stored in
+    // state. This should be the same as we had before calling $loaded->save().
+    /** @var \Drupal\Core\Entity\ContentEntityInterface $loaded_original */
+    $originalRevisionId = \Drupal::state()->get('entity_test.originalRevisionId');
+    $this->assertEquals($entity->getRevisionId(), $originalRevisionId);
+    $this->assertNotEquals($loaded->getRevisionId(), $originalRevisionId);
+
+    // The revision ID and original revision ID should be different for the two
+    // versions of the entity, but the same for a saved entity.
+    $this->assertNotEquals($loaded->getRevisionId(), $entity->getRevisionId());
+    $this->assertNotEquals($loaded->getOriginalRevisionId(), $entity->getOriginalRevisionId());
+    $this->assertEquals($entity->getRevisionId(), $entity->getOriginalRevisionId());
+    $this->assertEquals($loaded->getRevisionId(), $loaded->getOriginalRevisionId());
+
+    // Make a change to the loaded entity.
+    $loaded->set('name', 'dublin');
+
+    // The revision id and original revision id should still be the same.
+    $this->assertEquals($loaded->getRevisionId(), $loaded->getOriginalRevisionId());
+
+    $loaded->save();
+
+    // After saving, the original revision id set in
+    // entity_test_entity_presave() and returned from the entity should be the
+    // same and the entity's revision id because a new revision wasn't created,
+    // the existing revision was updated.
+    $originalRevisionId2 = \Drupal::state()->get('entity_test.originalRevisionId');
+    $this->assertEquals($loaded->getRevisionId(), $originalRevisionId2);
+    $this->assertEquals($loaded->getRevisionId(), $loaded->getOriginalRevisionId());
+
+    $duplicate = $loaded->createDuplicate();
+    $this->assertSame(NULL, $duplicate->getOriginalRevisionId());
+  }
+}