diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index cc60af2..de83cc3 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -2089,7 +2089,12 @@ function theme_table($variables) {
     drupal_add_library('system', 'drupal.tableheader');
     // Add 'sticky-enabled' class to the table to identify it for JS.
     // This is needed to target tables constructed by this function.
-    $attributes['class'][] = 'sticky-enabled';
+    if (isset($table_attributes['class'])) {
+      $table_attributes['class'][] = 'sticky-enabled';
+    }
+    else {
+      $table_attributes['class'] = array('sticky-enabled');
+    }
   }
   // If the table has headers and it should react responsively to columns hidden
   // with the classes represented by the constants RESPONSIVE_PRIORITY_MEDIUM
@@ -2098,7 +2103,12 @@ function theme_table($variables) {
     drupal_add_library('system', 'drupal.tableresponsive');
     // Add 'responsive-enabled' class to the table to identify it for JS.
     // This is needed to target tables constructed by this function.
-    $attributes['class'][] = 'responsive-enabled';
+    if (isset($table_attributes['class'])) {
+      $table_attributes['class'][] = 'responsive-enabled';
+    }
+    else {
+      $table_attributes['class'] = array('responsive-enabled');
+    }
   }
 
   $output = '<table' . new Attribute($attributes) . ">\n";
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
index d0c833a..5a14aaf 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockStorageUnitTest.php
@@ -138,11 +138,13 @@ protected function renderTests() {
     // Test the rendering of a block.
     $output = entity_view($entity, 'block');
     $expected = array();
-    $expected[] = '  <div id="block-test-block"  class="block block-block-test">';
-    $expected[] = '';
+    $expected[] = '<div id="block-test-block" class="block block-block-test">';
+    $expected[] = '  ';
     $expected[] = '    ';
+    $expected[] = '';
     $expected[] = '  <div class="content">';
-    $expected[] = '      </div>';
+    $expected[] = '   ';
+    $expected[] = '  </div>';
     $expected[] = '</div>';
     $expected[] = '';
     $expected_output = implode("\n", $expected);
@@ -155,12 +157,14 @@ protected function renderTests() {
     $entity->set('label', 'Powered by Bananas');
     $output = entity_view($entity, 'block');
     $expected = array();
-    $expected[] = '  <div id="block-test-block"  class="block block-block-test">';
-    $expected[] = '';
-    $expected[] = '    <h2 class="">Powered by Bananas</h2>';
+    $expected[] = '<div id="block-test-block" class="block block-block-test">';
     $expected[] = '  ';
+    $expected[] = '      <h2 class="">Powered by Bananas</h2>';
+    $expected[] = '    ';
+    $expected[] = '';
     $expected[] = '  <div class="content">';
-    $expected[] = '      </div>';
+    $expected[] = '   ';
+    $expected[] = '  </div>';
     $expected[] = '</div>';
     $expected[] = '';
     $expected_output = implode("\n", $expected);
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php
index c469eb6..7b49110 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockTemplateSuggestionsUnitTest.php
@@ -51,11 +51,8 @@ function testBlockThemeHookSuggestions() {
       'module' => $block->get('module'),
     );
     $variables['elements']['#children'] = '';
-    // Test adding a class to the block content.
-    $variables['content_attributes']['class'][] = 'test-class';
     template_preprocess_block($variables);
     $this->assertEqual($variables['theme_hook_suggestions'], array('block__footer', 'block__system', 'block__system_menu_block', 'block__system_menu_block__menu_admin', 'block__machinename'));
-    $this->assertEqual($variables['content_attributes']['class'], array('test-class', 'content'), 'Default .content class added to block content_attributes_array');
   }
 
 }