diff --git a/core/modules/comment/tests/src/Kernel/Migrate/d7/MigrateCommentTest.php b/core/modules/comment/tests/src/Kernel/Migrate/d7/MigrateCommentTest.php
index b5b873abb4..caa92b1553 100644
--- a/core/modules/comment/tests/src/Kernel/Migrate/d7/MigrateCommentTest.php
+++ b/core/modules/comment/tests/src/Kernel/Migrate/d7/MigrateCommentTest.php
@@ -105,6 +105,27 @@ public function testMigration() {
     $node = $comment->getCommentedEntity();
     $this->assertInstanceOf(NodeInterface::class, $node);
     $this->assertSame('2', $node->id());
+
+    // Comment migrated from Drupal 6 to Drupal 7 may have empty language
+    // property. This is invalid in Drupal 8. Test that these comments will have
+    // valid language after the migration.
+    $comment = Comment::load(4);
+    $this->assertInstanceOf(Comment::class, $comment);
+    $this->assertSame('Comment without language', $comment->getSubject());
+    $this->assertSame('1426781880', $comment->getCreatedTime());
+    $this->assertSame('1426781880', $comment->getChangedTime());
+    $this->assertTrue($comment->isPublished());
+    $this->assertSame('Bob', $comment->getAuthorName());
+    $this->assertSame('bob@local.host', $comment->getAuthorEmail());
+    $this->assertSame('A comment without language (migrated from Drupal 6)', $comment->comment_body->value);
+    $this->assertSame('filtered_html', $comment->comment_body->format);
+    $this->assertSame('drupal7.local', $comment->getHostname());
+    $this->assertSame('und', $comment->language()->getId());
+    $this->assertSame('10', $comment->field_integer->value);
+
+    $node = $comment->getCommentedEntity();
+    $this->assertInstanceOf(NodeInterface::class, $node);
+    $this->assertSame('1', $node->id());
   }
 
   /**
diff --git a/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php
index dc99489563..1231a7a377 100644
--- a/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php
+++ b/core/modules/comment/tests/src/Kernel/Plugin/migrate/source/d7/CommentTest.php
@@ -42,6 +42,24 @@ public function providerSource() {
         'language' => 'und',
       ],
     ];
+    $tests[1]['source_data']['comment'] = [
+      [
+        'cid' => '2',
+        'pid' => '0',
+        'nid' => '1',
+        'uid' => '1',
+        'subject' => 'A comment migrated from Drupal 6',
+        'hostname' => '::1',
+        'created' => '1421727535',
+        'changed' => '1421727535',
+        'status' => '1',
+        'thread' => '02/',
+        'name' => 'admin',
+        'mail' => '',
+        'homepage' => '',
+        'language' => '',
+      ],
+    ];
     $tests[0]['source_data']['node'] = [
       [
         'nid' => '1',
@@ -60,6 +78,7 @@ public function providerSource() {
         'translate' => '0',
       ],
     ];
+    $tests[1]['source_data']['node'] = $tests[0]['source_data']['node'];
     $tests[0]['source_data']['field_config'] = [
       [
         'id' => '1',
@@ -70,6 +89,7 @@ public function providerSource() {
         'translatable' => '1',
       ],
     ];
+    $tests[1]['source_data']['field_config'] = $tests[0]['source_data']['field_config'];
     $tests[0]['source_data']['field_config_instance'] = [
       [
         'id' => '14',
@@ -90,6 +110,7 @@ public function providerSource() {
         'deleted' => '0',
       ],
     ];
+    $tests[1]['source_data']['field_config_instance'] = $tests[0]['source_data']['field_config_instance'];
     $tests[0]['source_data']['field_data_comment_body'] = [
       [
         'entity_type' => 'comment',
@@ -103,6 +124,19 @@ public function providerSource() {
         'comment_body_format' => 'filtered_html',
       ],
     ];
+    $tests[1]['source_data']['field_data_comment_body'] = [
+      [
+        'entity_type' => 'comment',
+        'bundle' => 'comment_node_test_content_type',
+        'deleted' => '0',
+        'entity_id' => '2',
+        'revision_id' => '2',
+        'language' => 'und',
+        'delta' => '0',
+        'comment_body_value' => 'This is a comment migrated from Drupal 6',
+        'comment_body_format' => 'filtered_html',
+      ],
+    ];
     $tests[0]['source_data']['field_data_subject_field'] = [
       [
         'entity_type' => 'comment',
@@ -116,6 +150,19 @@ public function providerSource() {
         'subject_field_format' => NULL,
       ],
     ];
+    $tests[1]['source_data']['field_data_subject_field'] = [
+      [
+        'entity_type' => 'comment',
+        'bundle' => 'comment_node_test_content_type',
+        'deleted' => '0',
+        'entity_id' => '1',
+        'revision_id' => '1',
+        'language' => 'und',
+        'delta' => '0',
+        'subject_field_value' => 'A comment migrated from Drupal 6 (subject_field)',
+        'subject_field_format' => NULL,
+      ],
+    ];
     $tests[0]['source_data']['system'] = [
       [
         'name' => 'title',
@@ -123,6 +170,7 @@ public function providerSource() {
         'status' => 1,
       ],
     ];
+    $tests[1]['source_data']['system'] = $tests[0]['source_data']['system'];
 
     // The expected results.
     $tests[0]['expected_data'] = [
@@ -149,6 +197,30 @@ public function providerSource() {
         ],
       ],
     ];
+    $tests[1]['expected_data'] = [
+      [
+        'cid' => '2',
+        'pid' => '0',
+        'nid' => '1',
+        'uid' => '1',
+        'subject' => 'A comment migrated from Drupal 6',
+        'hostname' => '::1',
+        'created' => '1421727535',
+        'changed' => '1421727535',
+        'status' => '1',
+        'thread' => '02/',
+        'name' => 'admin',
+        'mail' => '',
+        'homepage' => '',
+        'language' => 'und',
+        'comment_body' => [
+          [
+            'value' => 'This is a comment migrated from Drupal 6',
+            'format' => 'filtered_html',
+          ],
+        ],
+      ],
+    ];
 
     return $tests;
   }
diff --git a/core/modules/migrate_drupal/tests/fixtures/drupal7.php b/core/modules/migrate_drupal/tests/fixtures/drupal7.php
index fafbed003a..664e1d981b 100644
--- a/core/modules/migrate_drupal/tests/fixtures/drupal7.php
+++ b/core/modules/migrate_drupal/tests/fixtures/drupal7.php
@@ -2701,6 +2701,22 @@
   'homepage' => '',
   'language' => 'is',
 ))
+->values(array(
+  'cid' => '4',
+  'pid' => '0',
+  'nid' => '1',
+  'uid' => '3',
+  'subject' => 'Comment without language',
+  'hostname' => 'drupal7.local',
+  'created' => '1426781880',
+  'changed' => '1426781880',
+  'status' => '1',
+  'thread' => '02/',
+  'name' => 'Bob',
+  'mail' => '',
+  'homepage' => '',
+  'language' => '',
+))
 ->execute();
 $connection->schema()->createTable('contact', array(
   'fields' => array(
@@ -3350,6 +3366,18 @@
   'created' => '1531663925',
   'changed' => '1531663925',
 ))
+->values(array(
+  'entity_type' => 'comment',
+  'entity_id' => '4',
+  'revision_id' => '4',
+  'language' => 'en',
+  'source' => '',
+  'uid' => '1',
+  'status' => '1',
+  'translate' => '0',
+  'created' => '1426781880',
+  'changed' => '1426781880',
+))
 ->values(array(
   'entity_type' => 'taxonomy_term',
   'entity_id' => '4',
@@ -5327,6 +5355,17 @@
   'comment_body_value' => 'This is a comment to an Icelandic translation.',
   'comment_body_format' => 'filtered_html',
 ))
+->values(array(
+  'entity_type' => 'comment',
+  'bundle' => 'comment_node_test_content_type',
+  'deleted' => '0',
+  'entity_id' => '4',
+  'revision_id' => '4',
+  'language' => 'und',
+  'delta' => '0',
+  'comment_body_value' => 'A comment without language (migrated from Drupal 6)',
+  'comment_body_format' => 'filtered_html',
+))
 ->execute();
 $connection->schema()->createTable('field_data_description_field', array(
   'fields' => array(
@@ -6927,6 +6966,16 @@
   'delta' => '0',
   'field_integer_value' => '1',
 ))
+->values(array(
+  'entity_type' => 'comment',
+  'bundle' => 'comment_node_test_content_type',
+  'deleted' => '0',
+  'entity_id' => '4',
+  'revision_id' => '4',
+  'language' => 'en',
+  'delta' => '0',
+  'field_integer_value' => '10',
+))
 ->values(array(
   'entity_type' => 'taxonomy_term',
   'bundle' => 'test_vocabulary',
@@ -10307,6 +10356,17 @@
   'subject_field_value' => 'Comment to IS translation',
   'subject_field_format' => NULL,
 ))
+->values(array(
+  'entity_type' => 'comment',
+  'bundle' => 'comment_node_test_content_type',
+  'deleted' => '0',
+  'entity_id' => '4',
+  'revision_id' => '4',
+  'language' => 'en',
+  'delta' => '0',
+  'subject_field_value' => 'Comment without language',
+  'subject_field_format' => NULL,
+))
 ->execute();
 $connection->schema()->createTable('field_data_taxonomy_forums', array(
   'fields' => array(
@@ -10818,6 +10878,17 @@
   'comment_body_value' => 'This is a comment to an Icelandic translation.',
   'comment_body_format' => 'filtered_html',
 ))
+->values(array(
+  'entity_type' => 'comment',
+  'bundle' => 'comment_node_test_content_type',
+  'deleted' => '0',
+  'entity_id' => '4',
+  'revision_id' => '4',
+  'language' => 'und',
+  'delta' => '0',
+  'comment_body_value' => 'A comment without language (migrated from Drupal 6)',
+  'comment_body_format' => 'filtered_html',
+))
 ->execute();
 $connection->schema()->createTable('field_revision_description_field', array(
   'fields' => array(
@@ -12423,6 +12494,16 @@
   'delta' => '0',
   'field_integer_value' => '99',
 ))
+->values(array(
+  'entity_type' => 'comment',
+  'bundle' => 'comment_node_test_content_type',
+  'deleted' => '0',
+  'entity_id' => '4',
+  'revision_id' => '4',
+  'language' => 'en',
+  'delta' => '0',
+  'field_integer_value' => '10',
+))
 ->values(array(
   'entity_type' => 'taxonomy_term',
   'bundle' => 'test_vocabulary',
@@ -15833,6 +15914,17 @@
   'subject_field_value' => 'Comment to IS translation',
   'subject_field_format' => NULL,
 ))
+->values(array(
+  'entity_type' => 'comment',
+  'bundle' => 'comment_node_test_content_type',
+  'deleted' => '0',
+  'entity_id' => '4',
+  'revision_id' => '4',
+  'language' => 'en',
+  'delta' => '0',
+  'subject_field_value' => 'Comment without language',
+  'subject_field_format' => NULL,
+))
 ->execute();
 $connection->schema()->createTable('field_revision_taxonomy_forums', array(
   'fields' => array(
@@ -41709,11 +41801,11 @@
 ))
 ->values(array(
   'nid' => '1',
-  'cid' => '1',
-  'last_comment_timestamp' => '1421727536',
+  'cid' => '4',
+  'last_comment_timestamp' => '1426781880',
   'last_comment_name' => '',
-  'last_comment_uid' => '1',
-  'comment_count' => '1',
+  'last_comment_uid' => '3',
+  'comment_count' => '2',
 ))
 ->values(array(
   'nid' => '3',
diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/d7/Upgrade7Test.php b/core/modules/migrate_drupal_ui/tests/src/Functional/d7/Upgrade7Test.php
index ba16905e72..579d640e27 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/d7/Upgrade7Test.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/d7/Upgrade7Test.php
@@ -64,7 +64,7 @@ protected function getEntityCounts() {
       'block' => 25,
       'block_content' => 1,
       'block_content_type' => 1,
-      'comment' => 3,
+      'comment' => 4,
       // The 'standard' profile provides the 'comment' comment type, and the
       // migration creates 6 comment types, one per node type.
       'comment_type' => 7,
@@ -111,7 +111,7 @@ protected function getEntityCounts() {
   protected function getEntityCountsIncremental() {
     $counts = $this->getEntityCounts();
     $counts['block_content'] = 2;
-    $counts['comment'] = 4;
+    $counts['comment'] = 5;
     $counts['file'] = 4;
     $counts['menu_link_content'] = 13;
     $counts['node'] = 7;