diff --git a/core/modules/block/lib/Drupal/block/BlockListController.php b/core/modules/block/lib/Drupal/block/BlockListController.php
index 697f09b..944b778 100644
--- a/core/modules/block/lib/Drupal/block/BlockListController.php
+++ b/core/modules/block/lib/Drupal/block/BlockListController.php
@@ -343,8 +343,9 @@ public function buildForm(array $form, array &$form_state) {
     });
     foreach ($plugins as $plugin_id => $plugin_definition) {
       $category = String::checkPlain($plugin_definition['category']);
-      if (!isset($form['place_blocks']['list'][$category])) {
-        $form['place_blocks']['list'][$category] = array(
+      $category_key = 'category-' . $category;
+      if (!isset($form['place_blocks']['list'][$category_key])) {
+        $form['place_blocks']['list'][$category_key] = array(
           '#type' => 'details',
           '#title' => $category,
           'content' => array(
@@ -358,7 +359,7 @@ public function buildForm(array $form, array &$form_state) {
           ),
         );
       }
-      $form['place_blocks']['list'][$category]['content']['#links'][$plugin_id] = array(
+      $form['place_blocks']['list'][$category_key]['content']['#links'][$plugin_id] = array(
         'title' => $plugin_definition['admin_label'],
         'href' => 'admin/structure/block/add/' . $plugin_id . '/' . $this->theme,
         'attributes' => array(
diff --git a/core/modules/block/lib/Drupal/block/Tests/Views/DisplayBlockTest.php b/core/modules/block/lib/Drupal/block/Tests/Views/DisplayBlockTest.php
index 668bd77..6e1899b 100644
--- a/core/modules/block/lib/Drupal/block/Tests/Views/DisplayBlockTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/Views/DisplayBlockTest.php
@@ -66,7 +66,7 @@ public function testBlockCategory() {
     // Test that the block was given a default category corresponding to its
     // base table.
     $arguments = array(
-      ':id' => 'edit-views-test-data',
+      ':id' => 'edit-category-views-test-data',
       ':li_class' => 'views-block' . drupal_html_class($edit['id']) . '-block-1',
       ':href' => url('admin/structure/block/add/views_block:' . $edit['id'] . '-block_1/stark'),
       ':text' => $edit['label'],
@@ -85,7 +85,7 @@ public function testBlockCategory() {
     $link = $this->xpath('//a[@id="views-block-1-block-category" and normalize-space(text())=:label]', array(':label' => $label));
     $this->assertTrue(!empty($link));
     $this->clickLink($label);
-    $category = $this->randomString();
+    $category = '#' . $this->randomString();
     $this->drupalPostForm(NULL, array('block_category' => $category), t('Apply'));
 
     // Clone the block after changing the category.
@@ -95,14 +95,14 @@ public function testBlockCategory() {
     $this->drupalPostForm(NULL, array(), t('Save'));
 
     // Test that the blocks are listed under the correct categories.
-    $category_id = drupal_html_id('edit-' . String::checkPlain($category));
+    $category_id = drupal_html_id('edit-category-' . String::checkPlain($category));
     $arguments[':id'] = $category_id;
     $this->drupalGet('admin/structure/block');
     $elements = $this->xpath('//details[@id=:id]//li[contains(@class, :li_class)]/a[contains(@href, :href) and text()=:text]', $arguments);
     $this->assertTrue(!empty($elements), 'The test block appears in the custom category.');
 
     $arguments = array(
-      ':id' => 'edit-views-test-data',
+      ':id' => 'edit-category-views-test-data',
       ':li_class' => 'views-block' . drupal_html_class($edit['id']) . '-block-2',
       ':href' => url('admin/structure/block/add/views_block:' . $edit['id'] . '-block_2/stark'),
       ':text' => $edit['label'],