diff -u b/core/modules/migrate_drupal/tests/fixtures/drupal6.php b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
--- b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
+++ b/core/modules/migrate_drupal/tests/fixtures/drupal6.php
@@ -3422,7 +3422,7 @@
   'field_test_imagefield_fid' => NULL,
   'field_test_imagefield_list' => NULL,
   'field_test_imagefield_data' => NULL,
-  'field_test_text_single_checkbox2_value' => 'Off',
+  'field_test_text_single_checkbox2_value' => NULL,
 ))
 ->execute();
 
diff -u b/core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeTest.php b/core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeTest.php
--- b/core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeTest.php
+++ b/core/modules/node/tests/src/Kernel/Migrate/d6/MigrateNodeTest.php
@@ -85,7 +85,8 @@
     $this->assertSame('Buy it now', $node->field_test_link->title);
     $this->assertSame(['attributes' => ['target' => '_blank']], $node->field_test_link->options);
 
-    // Rerun migration with invalid link attributes and a different URL and
+    // Rerun migration with two source database changes.
+    // 1. Add an invalid link attributes and a different URL and
     // title. If only the attributes are changed the error does not occur.
     Database::getConnection('default', 'migrate')
       ->update('content_type_story')
@@ -98,12 +99,27 @@
       ->condition('vid', '3')
       ->execute();
 
+    // 2. Add an leading slash to an internal link.
+    Database::getConnection('default', 'migrate')
+      ->update('content_type_story')
+      ->fields([
+        'field_test_link_url' => '/node/10',
+      ])
+      ->condition('nid', '9')
+      ->condition('vid', '12')
+      ->execute();
+
     $this->rerunMigration();
     $node = Node::load(2);
     $this->assertIdentical('https://www.drupal.org/node/2127611', $node->field_test_link->uri);
     $this->assertIdentical('Migrate API in Drupal 8', $node->field_test_link->title);
     $this->assertIdentical([], $node->field_test_link->options['attributes']);
 
+    $node = Node::load(9);
+    $this->assertSame('internal:/node/10', $node->field_test_link->uri);
+    $this->assertSame('Buy it now', $node->field_test_link->title);
+    $this->assertSame(['attributes' => ['target' => '_blank']], $node->field_test_link->options);
+
     // Test that we can re-import using the EntityContentBase destination.
     $title = $this->rerunMigration();
     $node = Node::load(2);