diff --git a/core/lib/Drupal/Core/Messenger/LegacyMessenger.php b/core/lib/Drupal/Core/Messenger/LegacyMessenger.php
index bdc66ffe39..b1482a8e1c 100644
--- a/core/lib/Drupal/Core/Messenger/LegacyMessenger.php
+++ b/core/lib/Drupal/Core/Messenger/LegacyMessenger.php
@@ -34,7 +34,7 @@ class LegacyMessenger implements MessengerInterface {
    * {@inheritdoc}
    */
   public function addError($message, $repeat = FALSE) {
-    return $this->addMessage($message, static::TYPE_ERROR);
+    return $this->addMessage($message, static::TYPE_ERROR, $repeat);
   }
 
   /**
@@ -67,14 +67,14 @@ public function addMessage($message, $type = self::TYPE_STATUS, $repeat = FALSE)
    * {@inheritdoc}
    */
   public function addStatus($message, $repeat = FALSE) {
-    return $this->addMessage($message, static::TYPE_STATUS);
+    return $this->addMessage($message, static::TYPE_STATUS, $repeat);
   }
 
   /**
    * {@inheritdoc}
    */
   public function addWarning($message, $repeat = FALSE) {
-    return $this->addMessage($message, static::TYPE_WARNING);
+    return $this->addMessage($message, static::TYPE_WARNING, $repeat);
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Messenger/Messenger.php b/core/lib/Drupal/Core/Messenger/Messenger.php
index b8b6c3ddf3..c0949438cc 100644
--- a/core/lib/Drupal/Core/Messenger/Messenger.php
+++ b/core/lib/Drupal/Core/Messenger/Messenger.php
@@ -43,7 +43,7 @@ public function __construct(FlashBagInterface $flash_bag, KillSwitch $killSwitch
    * {@inheritdoc}
    */
   public function addError($message, $repeat = FALSE) {
-    return $this->addMessage($message, static::TYPE_ERROR);
+    return $this->addMessage($message, static::TYPE_ERROR, $repeat);
   }
 
   /**
@@ -70,14 +70,14 @@ public function addMessage($message, $type = self::TYPE_STATUS, $repeat = FALSE)
    * {@inheritdoc}
    */
   public function addStatus($message, $repeat = FALSE) {
-    return $this->addMessage($message, static::TYPE_STATUS);
+    return $this->addMessage($message, static::TYPE_STATUS, $repeat);
   }
 
   /**
    * {@inheritdoc}
    */
   public function addWarning($message, $repeat = FALSE) {
-    return $this->addMessage($message, static::TYPE_WARNING);
+    return $this->addMessage($message, static::TYPE_WARNING, $repeat);
   }
 
   /**
diff --git a/core/tests/Drupal/KernelTests/Core/Messenger/LegacyMessengerTest.php b/core/tests/Drupal/KernelTests/Core/Messenger/LegacyMessengerTest.php
index 13f10e9c2e..92351bc224 100644
--- a/core/tests/Drupal/KernelTests/Core/Messenger/LegacyMessengerTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Messenger/LegacyMessengerTest.php
@@ -81,4 +81,25 @@ public function testMessages() {
     $this->assertContains('Cheetah', $messages[MessengerInterface::TYPE_WARNING]);
   }
 
+
+  public function testRepeatedMessages() {
+    // Add repeated messages of different types.
+    $messenger = \Drupal::messenger();
+
+    $messenger->addError('Foo', TRUE);
+    $messenger->addError('Foo', TRUE);
+
+    $messenger->addStatus('Bar', TRUE);
+    $messenger->addStatus('Bar', TRUE);
+
+    $messenger->addWarning('Fiz', TRUE);
+    $messenger->addWarning('Fiz', TRUE);
+
+    // Verify that all the messages are present and accounted for.
+    $messages = $messenger->all();
+    $this->assertCount(2, $messages[MessengerInterface::TYPE_STATUS]);
+    $this->assertCount(2, $messages[MessengerInterface::TYPE_WARNING]);
+    $this->assertCount(2, $messages[MessengerInterface::TYPE_ERROR]);
+  }
+
 }
diff --git a/core/tests/Drupal/KernelTests/Core/Messenger/MessengerKernelTest.php b/core/tests/Drupal/KernelTests/Core/Messenger/MessengerKernelTest.php
new file mode 100644
index 0000000000..b3aaad6b3d
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Messenger/MessengerKernelTest.php
@@ -0,0 +1,155 @@
+<?php
+
+namespace Drupal\KernelTests\Core\Messenger;
+
+use Drupal\Core\Messenger\MessengerInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\Core\Render\Markup;
+
+/**
+ * @group Messenger
+ * @coversDefaultClass \Drupal\Core\Messenger\Messenger
+ */
+class MessengerKernelTest extends KernelTestBase {
+
+  /**
+   * The messenger under test.
+   *
+   * @var \Drupal\Core\Messenger\MessengerInterface
+   */
+  protected $messenger;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp() {
+    parent::setUp();
+    $this->messenger = \Drupal::service('messenger');
+  }
+
+  /**
+   * @covers ::addStatus
+   * @covers ::deleteByType
+   * @covers ::messagesByType
+   */
+  public function testRemoveSingleMessage() {
+
+    // Set two messages.
+    $this->messenger->addStatus('First message (removed).');
+    $this->messenger->addStatus(t('Second message with <em>markup!</em> (not removed).'));
+    $messages = $this->messenger->deleteByType(MessengerInterface::TYPE_STATUS);
+    // Remove the first.
+    unset($messages[0]);
+
+    // Re-add the second.
+    foreach ($messages as $message) {
+      $this->messenger->addStatus($message);
+    }
+
+    // Check we only have the second one.
+    $this->assertCount(1, $this->messenger->messagesByType(MessengerInterface::TYPE_STATUS));
+    $this->assertContains('Second message with <em>markup!</em> (not removed).', $this->messenger->deleteByType(MessengerInterface::TYPE_STATUS));
+
+  }
+
+  /**
+   * Tests we don't add duplicates.
+   *
+   * @covers ::all
+   * @covers ::addStatus
+   * @covers ::addWarning
+   * @covers ::addError
+   * @covers ::deleteByType
+   * @covers ::deleteAll
+   */
+  public function testAddNoDuplicates() {
+
+    $this->messenger->addStatus('Non Duplicated status message');
+    $this->messenger->addStatus('Non Duplicated status message');
+
+    $this->assertCount(1, $this->messenger->messagesByType(MessengerInterface::TYPE_STATUS));
+
+    $this->messenger->addWarning('Non Duplicated warning message');
+    $this->messenger->addWarning('Non Duplicated warning message');
+
+    $this->assertCount(1, $this->messenger->messagesByType(MessengerInterface::TYPE_WARNING));
+
+    $this->messenger->addError('Non Duplicated error message');
+    $this->messenger->addError('Non Duplicated error message');
+
+    $this->assertCount(1, $this->messenger->messagesByType(MessengerInterface::TYPE_ERROR));
+
+    // Check getting all messages.
+    $messages = $this->messenger->all();
+    $this->assertCount(3, $messages);
+    $this->assertArrayHasKey(MessengerInterface::TYPE_STATUS, $messages);
+    $this->assertArrayHasKey(MessengerInterface::TYPE_WARNING, $messages);
+    $this->assertArrayHasKey(MessengerInterface::TYPE_ERROR, $messages);
+
+    // Check deletion.
+    $this->messenger->deleteAll();
+    $this->assertCount(0, $this->messenger->messagesByType(MessengerInterface::TYPE_STATUS));
+    $this->assertCount(0, $this->messenger->messagesByType(MessengerInterface::TYPE_WARNING));
+    $this->assertCount(0, $this->messenger->messagesByType(MessengerInterface::TYPE_ERROR));
+
+  }
+
+  /**
+   * Tests we do add duplicates with repeat flag.
+   *
+   * @covers ::addStatus
+   * @covers ::addWarning
+   * @covers ::addError
+   * @covers ::deleteByType
+   */
+  public function testAddWithDuplicates() {
+
+    $this->messenger->addStatus('Duplicated status message', TRUE);
+    $this->messenger->addStatus('Duplicated status message', TRUE);
+
+    $this->assertCount(2, $this->messenger->deleteByType(MessengerInterface::TYPE_STATUS));
+
+    $this->messenger->addWarning('Duplicated warning message', TRUE);
+    $this->messenger->addWarning('Duplicated warning message', TRUE);
+
+    $this->assertCount(2, $this->messenger->deleteByType(MessengerInterface::TYPE_WARNING));
+
+    $this->messenger->addError('Duplicated error message', TRUE);
+    $this->messenger->addError('Duplicated error message', TRUE);
+
+    $this->assertCount(2, $this->messenger->deleteByType(MessengerInterface::TYPE_ERROR));
+
+  }
+
+  /**
+   * Test adding markup.
+   *
+   * @covers ::addStatus
+   * @covers ::deleteByType
+   * @covers ::messagesByType
+   */
+  public function testAddMarkup() {
+
+    // Add a Markup message.
+    $this->messenger->addStatus(Markup::create('Markup with <em>markup!</em>'));
+    // Test duplicate Markup messages.
+    $this->messenger->addStatus(Markup::create('Markup with <em>markup!</em>'));
+
+    $this->assertCount(1, $this->messenger->messagesByType(MessengerInterface::TYPE_STATUS));
+
+    // Ensure that multiple Markup messages work.
+    $this->messenger->addStatus(Markup::create('Markup2 with <em>markup!</em>'));
+
+    $this->assertCount(2, $this->messenger->deleteByType(MessengerInterface::TYPE_STATUS));
+
+    // Test mixing of types.
+    $this->messenger->addStatus(Markup::create('Non duplicate Markup / string.'));
+    $this->messenger->addStatus('Non duplicate Markup / string.');
+    $this->messenger->addStatus(Markup::create('Duplicate Markup / string.'), TRUE);
+    $this->messenger->addStatus('Duplicate Markup / string.', TRUE);
+
+    $this->assertCount(3, $this->messenger->deleteByType(MessengerInterface::TYPE_STATUS));
+
+  }
+
+}