diff --git a/core/modules/block/lib/Drupal/block/BlockListController.php b/core/modules/block/lib/Drupal/block/BlockListController.php
index 0a3285b..b55bd45 100644
--- a/core/modules/block/lib/Drupal/block/BlockListController.php
+++ b/core/modules/block/lib/Drupal/block/BlockListController.php
@@ -393,7 +393,7 @@ public function getOperations(EntityInterface $entity) {
   public function validateForm(array &$form, array &$form_state) {
     $content = $form_state['values']['edited_theme'] . '_content';
     if (isset($form_state['values']['blocks'][$content]['region']) && $form_state['values']['blocks'][$content]['region'] == -1) {
-      form_set_error('blocks][' . $content, t('Main page content block needs to be placed in some region.'));
+      form_set_error('blocks][' . $content, t('Main page content block needs to be placed in a region.'));
     }
   }
 
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockUiTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockUiTest.php
index bb0a6ee..3db5be0 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockUiTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockUiTest.php
@@ -130,18 +130,18 @@ function testBlockAdminUiPage() {
   }
 
   /**
-   * Tests that the main page content block needs to be assigned in some region.
+   * Tests that the main page content block needs to be assigned to a region.
    */
   public function testSystemMainContentBlockAssigned() {
     // Try to disable main page content block.
     $edit = array('blocks[' . $this->currentTheme . '_content][region]' => -1);
     $this->drupalPostForm('admin/structure/block', $edit, t('Save blocks'));
-    $this->assertText(t('Main page content block needs to be placed in some region.'), 'Failed to disable main page content block.');
+    $this->assertText(t('Main page content block needs to be placed in a region.'), 'Failed to disable main page content block.');
 
-    // Try to set main page content block in main content region.
+    // Try to set main page content block in the content region.
     $edit = array('blocks[' . $this->currentTheme . '_content][region]' => 'content');
     $this->drupalPostForm('admin/structure/block', $edit, t('Save blocks'));
-    $this->assertText(t('The block settings have been updated.'), 'Main page content block successfully moved to Content region.');
+    $this->assertText(t('The block settings have been updated.'), 'Main page content block successfully moved to content region.');
   }
 
   /**