diff -u b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
--- b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/mysql/Schema.php
@@ -306,7 +306,7 @@
    *   List of shortened indexes.
    */
   protected function getNormalizedIndexes(array $spec) {
-    $indexes = parent::getNormalizedIndexes($spec);
+    $indexes = isset($spec['indexes']) ? $spec['indexes'] : [];
     foreach ($indexes as $index_name => $index_fields) {
       foreach ($index_fields as $index_key => $index_field) {
         // Get the name of the field from the index specification.
diff -u b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
--- b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
@@ -648,8 +648,6 @@
       throw new SchemaObjectExistsException(t("Cannot add index @name to table @table: index already exists.", array('@table' => $table, '@name' => $name)));
     }
 
-    $spec['indexes'][$name] = $fields;
-
     $this->connection->query($this->_createIndexSql($table, $name, $fields));
     $this->resetTableInformation($table);
   }
@@ -784,9 +782,9 @@
     }
     if (isset($new_keys['indexes'])) {
       foreach ($new_keys['indexes'] as $name => $fields) {
-        // Even $new_keys is not a full schema it still has 'indexes' and so is
-        // a partial schema. Technically addIndex() doesn't do anything with it
-        // so passing an empty array would work as well.
+        // Even though $new_keys is not a full schema it still has 'indexes' and
+        // so is a partial schema. Technically addIndex() doesn't do anything
+        // with it so passing an empty array would work as well.
         $this->addIndex($table, $name, $fields, $new_keys);
       }
     }
diff -u b/core/lib/Drupal/Core/Database/Driver/sqlite/Schema.php b/core/lib/Drupal/Core/Database/Driver/sqlite/Schema.php
--- b/core/lib/Drupal/Core/Database/Driver/sqlite/Schema.php
+++ b/core/lib/Drupal/Core/Database/Driver/sqlite/Schema.php
@@ -593,9 +593,8 @@
       throw new SchemaObjectExistsException(t("Cannot add index @name to table @table: index already exists.", array('@table' => $table, '@name' => $name)));
     }
 
-    $spec['indexes'][$name] = $fields;
-
-    $statements = $this->createIndexSql($table, $spec);
+    $schema['indexes'][$name] = $fields;
+    $statements = $this->createIndexSql($table, $schema);
     foreach ($statements as $statement) {
       $this->connection->query($statement);
     }
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
@@ -462,15 +462,2 @@
   /**
-   * Gets normalized indexes from a table specification.
-   *
-   * @param array $spec
-   *   The table specification.
-   *
-   * @return array
-   *   List of shortened indexes.
-   */
-  protected function getNormalizedIndexes(array $spec) {
-    return isset($spec['indexes']) ? $spec['indexes'] : [];
-  }
-
-  /**
    * Drop an index.