diff -u b/core/lib/Drupal/Core/Database/Schema.php b/core/lib/Drupal/Core/Database/Schema.php
--- b/core/lib/Drupal/Core/Database/Schema.php
+++ b/core/lib/Drupal/Core/Database/Schema.php
@@ -428,11 +428,11 @@
   /**
    * Validates whether the index is valid.
    *
-   * This method ensures that the table exists, that the new index was specified
-   * and that there is no index with the same name yet.
+   * This method ensures that the table exists and that there is no index with
+   * the same name yet.
    *
    * @param string $table
-   *   The table of the index name.
+   *   The name of the table the index will be added to.
    * @param string $name
    *   The name of the index.
    *
diff -u b/core/modules/system/src/Tests/Database/SchemaTest.php b/core/modules/system/src/Tests/Database/SchemaTest.php
--- b/core/modules/system/src/Tests/Database/SchemaTest.php
+++ b/core/modules/system/src/Tests/Database/SchemaTest.php
@@ -302,7 +302,6 @@
     $table_specification_with_new_index['indexes']['test_separate'] = [['test_field_text', 200]];
 
     // Ensure that the exceptions of addIndex are thrown as expected.
-
     try {
       $schema_object->addIndex('test_table_index_length', 'test_separate', [['test_field_text', 200]], $table_specification);
       $this->fail('\Drupal\Core\Database\SchemaObjectExistsException exception missed.');