diff --git a/core/modules/block/block.install b/core/modules/block/block.install
index 305f438..106815c 100644
--- a/core/modules/block/block.install
+++ b/core/modules/block/block.install
@@ -124,29 +124,5 @@ function block_update_8003() {
 }
 
 /**
- * Disable blocks that are placed into the "disabled" region.
- */
-function block_update_8004() {
-  // Find all blocks in the disabled region.
-  /** @var \Drupal\block\BlockInterface[] $blocks */
-  $block_ids = \Drupal::entityManager()
-    ->getStorage('block')
-    ->getQuery()
-    ->condition('region', -1)
-    ->execute();
-
-  $config_factory = \Drupal::configFactory();
-
-  // Disable each block and assign them to the default region.
-  foreach ($block_ids as $block_id) {
-    $block_config = $config_factory->getEditable('block.block.' . $block_id);
-    $block_config
-      ->set('region', system_default_region($block_config->get('theme')))
-      ->set('status', FALSE)
-      ->save();
-  }
-}
-
-/**
  * @} End of "addtogroup updates-8.0.0-beta".
  */
diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index 5b30b4a..e415524 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -144,8 +144,10 @@ function block_rebuild() {
       $blocks = \Drupal::entityTypeManager()->getStorage('block')->loadByProperties(['theme' => $theme]);
       foreach ($blocks as $block_id => $block) {
         // Disable blocks in invalid regions.
-        if (!isset($regions[$block->getRegion()]) && $block->status()) {
-          drupal_set_message(t('The block %info was assigned to the invalid region %region and has been disabled.', ['%info' => $block_id, '%region' => $block->getRegion()]), 'warning');
+        if (!isset($regions[$block->getRegion()])) {
+          if ($block->status()) {
+            drupal_set_message(t('The block %info was assigned to the invalid region %region and has been disabled.', ['%info' => $block_id, '%region' => $block->getRegion()]), 'warning');
+          }
           $block
             ->setRegion(system_default_region($theme))
             ->disable()
diff --git a/core/modules/block/block.post_update.php b/core/modules/block/block.post_update.php
index f208f65..7bab413 100644
--- a/core/modules/block/block.post_update.php
+++ b/core/modules/block/block.post_update.php
@@ -75,5 +75,12 @@ function block_post_update_disable_blocks_with_missing_contexts() {
 }
 
 /**
+ * Disable blocks that are placed into the "disabled" region.
+ */
+function block_post_update_disabled_region_update() {
+  // An empty update will flush caches, forcing block_rebuild() to run.
+}
+
+/**
  * @} End of "addtogroup updates-8.0.0-beta".
  */
diff --git a/core/modules/block/src/Entity/Block.php b/core/modules/block/src/Entity/Block.php
index 1a0c82c..63b5205 100644
--- a/core/modules/block/src/Entity/Block.php
+++ b/core/modules/block/src/Entity/Block.php
@@ -330,4 +330,21 @@ public function createDuplicateBlock($new_id = NULL, $new_theme = NULL) {
     return $duplicate;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function preSave(EntityStorageInterface $storage) {
+    parent::preSave($storage);
+
+    // Ensure the region is valid to mirror the behavior of block_rebuild().
+    // This is done primarily for backwards compatibility support of
+    // \Drupal\block\BlockInterface::BLOCK_REGION_NONE.
+    $regions = system_region_list($this->theme);
+    if (!isset($regions[$this->region]) && $this->status()) {
+      $this
+        ->setRegion(system_default_region($this->theme))
+        ->disable();
+    }
+  }
+
 }
diff --git a/core/modules/block/src/Tests/Update/BlockRemoveDisabledRegionUpdateTest.php b/core/modules/block/src/Tests/Update/BlockRemoveDisabledRegionUpdateTest.php
index c359b3b..0d9826f 100644
--- a/core/modules/block/src/Tests/Update/BlockRemoveDisabledRegionUpdateTest.php
+++ b/core/modules/block/src/Tests/Update/BlockRemoveDisabledRegionUpdateTest.php
@@ -53,10 +53,10 @@ public function testUpdateHookN() {
       [':block' => 'edit-blocks-pagetitle-1', ':status' => 'block-disabled', ':region' => 'header']);
     $this->assertTrue(!empty($element));
 
-    // Verify that an enabled block is in the default region.
+    // Verify that an enabled block is now disabled and in the default region.
     $this->drupalGet('admin/structure/block');
     $element = $this->xpath("//tr[contains(@data-drupal-selector, :block) and contains(@class, :status)]//select/option[@selected and @value=:region]",
-      [':block' => 'edit-blocks-pagetitle-2', ':status' => 'block-enabled', ':region' => 'header']);
+      [':block' => 'edit-blocks-pagetitle-2', ':status' => 'block-disabled', ':region' => 'header']);
     $this->assertTrue(!empty($element));
 
   }
diff --git a/core/modules/block/tests/src/Kernel/BlockRebuildTest.php b/core/modules/block/tests/src/Kernel/BlockRebuildTest.php
index e2d555d..39ed44e 100644
--- a/core/modules/block/tests/src/Kernel/BlockRebuildTest.php
+++ b/core/modules/block/tests/src/Kernel/BlockRebuildTest.php
@@ -29,6 +29,7 @@ protected function setUp() {
     parent::setUp();
 
     $this->container->get('theme_installer')->install(['stable', 'classy']);
+    $this->container->get('config.factory')->getEditable('system.theme')->set('default', 'classy')->save();
   }
 
   /**
@@ -55,7 +56,7 @@ public function testRebuildNoBlocks() {
    * @covers ::block_rebuild
    */
   public function testRebuildNoInvalidBlocks() {
-    $this->placeBlock('system_powered_by_block', ['region' => 'content', 'theme' => 'classy']);
+    $this->placeBlock('system_powered_by_block', ['region' => 'content']);
 
     block_rebuild();
     $messages = drupal_get_messages();
@@ -66,20 +67,38 @@ public function testRebuildNoInvalidBlocks() {
    * @covers ::block_rebuild
    */
   public function testRebuildInvalidBlocks() {
-    $this->placeBlock('system_powered_by_block', ['region' => 'content', 'theme' => 'classy']);
-    $block = $this->placeBlock('system_powered_by_block', ['region' => 'INVALID', 'theme' => 'classy']);
-    $this->assertSame('INVALID', $block->getRegion());
-    $this->assertTrue($block->status());
+    $this->placeBlock('system_powered_by_block', ['region' => 'content']);
+    $block1 = $this->placeBlock('system_powered_by_block');
+    $block2 = $this->placeBlock('system_powered_by_block');
+    $block2->disable()->save();
+    // Use the config API directly to bypass Block::preSave().
+    \Drupal::configFactory()->getEditable('block.block.' . $block1->id())->set('region', 'INVALID')->save();
+    \Drupal::configFactory()->getEditable('block.block.' . $block2->id())->set('region', 'INVALID')->save();
+
+    // Reload block entities.
+    $block1 = Block::load($block1->id());
+    $block2 = Block::load($block2->id());
+
+    $this->assertSame('INVALID', $block1->getRegion());
+    $this->assertTrue($block1->status());
+    $this->assertSame('INVALID', $block2->getRegion());
+    $this->assertFalse($block2->status());
 
     block_rebuild();
-    // Reload block entity.
-    $block = Block::load($block->id());
+
+    // Reload block entities.
+    $block1 = Block::load($block1->id());
+    $block2 = Block::load($block2->id());
 
     $messages = drupal_get_messages();
-    $expected = ['warning' => [new TranslatableMarkup('The block %info was assigned to the invalid region %region and has been disabled.', ['%info' => $block->id(), '%region' => 'INVALID'])]];
+    $expected = ['warning' => [new TranslatableMarkup('The block %info was assigned to the invalid region %region and has been disabled.', ['%info' => $block1->id(), '%region' => 'INVALID'])]];
     $this->assertEquals($expected, $messages);
-    $this->assertSame(system_default_region('classy'), $block->getRegion());
-    $this->assertFalse($block->status());
+
+    $default_region = system_default_region('classy');
+    $this->assertSame($default_region, $block1->getRegion());
+    $this->assertFalse($block1->status());
+    $this->assertSame($default_region, $block2->getRegion());
+    $this->assertFalse($block2->status());
   }
 
 }
diff --git a/core/modules/system/tests/fixtures/update/block.block.secondtestfor2513534.yml b/core/modules/system/tests/fixtures/update/block.block.secondtestfor2513534.yml
index b1dbbae..2999cab 100644
--- a/core/modules/system/tests/fixtures/update/block.block.secondtestfor2513534.yml
+++ b/core/modules/system/tests/fixtures/update/block.block.secondtestfor2513534.yml
@@ -6,7 +6,7 @@ dependencies:
     - bartik
 id: pagetitle_2
 theme: bartik
-region: header
+region: '-1'
 weight: null
 provider: null
 plugin: page_title_block