diff --git a/core/lib/Drupal/Core/Database/Database.php b/core/lib/Drupal/Core/Database/Database.php
index 7623ce6..7ccb5d0 100644
--- a/core/lib/Drupal/Core/Database/Database.php
+++ b/core/lib/Drupal/Core/Database/Database.php
@@ -127,7 +127,7 @@
    * @param string $key
    *   The database connection key for which we want to log.
    *
-   * @return array
+   * @return mixed[]
    *   The query log for the specified logging key and connection.
    *
    * @see \Drupal\Core\Database\Log
@@ -191,7 +191,7 @@
    * Sets the active connection to the specified key.
    *
    * @param string $key
-   * Database connection key in settings.php which should be set as active.
+   *   Database connection key in settings.php which should be set as active.
    *
    * @return string|null
    *   The previous database connection key.
@@ -268,7 +268,7 @@
    * @param string $key
    *   (optional) The connection key for which to return information.
    *
-   * @return array|null
+   * @return array[]|null
    */
   final public static function getConnectionInfo($key = 'default') {
     if (!empty(self::$databaseInfo[$key])) {
@@ -279,7 +279,7 @@
   /**
    * Gets connection information for all available databases.
    *
-   * @return array
+   * @return array[]
    */
   final public static function getAllConnectionInfo() {
     return self::$databaseInfo;
@@ -458,7 +458,7 @@ public static function ignoreTarget($key, $target) {
    * @param string $root
    *   The root directory of the Drupal installation.
    *
-   * @return array
+   * @return mixed[]
    *   The database connection info.
    *
    * @throws \InvalidArgumentException
diff --git a/core/lib/Drupal/Core/Database/Log.php b/core/lib/Drupal/Core/Database/Log.php
index 2094a56..556617e 100644
--- a/core/lib/Drupal/Core/Database/Log.php
+++ b/core/lib/Drupal/Core/Database/Log.php
@@ -107,7 +107,7 @@ public function end($logging_key) {
   /**
    * Log a query to all active logging keys.
    *
-   * @param StatementInterface $statement
+   * @param \Drupal\Core\Database\StatementInterface $statement
    *   The prepared statement object to log.
    * @param array args
    *   The arguments passed to the statement object.
@@ -137,7 +137,7 @@ public function log(StatementInterface $statement, $args, $time) {
    * the query builders.
    *
    * @link http://www.php.net/debug_backtrace
-   * @return array
+   * @return mixed []
    *   This method returns a stack trace entry similar to that generated by
    *   debug_backtrace(). However, it flattens the trace entry and the trace
    *   entry before it so that we get the function and args of the function that
diff --git a/core/lib/Drupal/Core/Database/Schema.php b/core/lib/Drupal/Core/Database/Schema.php
index f2490e8..7905673 100644
--- a/core/lib/Drupal/Core/Database/Schema.php
+++ b/core/lib/Drupal/Core/Database/Schema.php
@@ -62,7 +62,6 @@ public function __construct($connection) {
   /**
    * Implements the magic __clone function.
    *
-   * @return string
    */
   public function __clone() {
     $this->uniqueIdentifier = uniqid('', TRUE);
@@ -93,7 +92,7 @@ public function nextPlaceholder() {
    * @param bool $add_prefix
    *   TRUE, if the given table name should be prefixed. FALSE, otherwise.
    *
-   * @return array
+   * @return mixed[]
    *   A keyed array with information about the schema, table name and prefix.
    */
   protected function getPrefixInfo($table = 'default', $add_prefix = TRUE) {
@@ -280,7 +279,7 @@ public function fieldExists($table, $column) {
    * its own normalized field type names. This function returns a driver-specific
    * mapping table from Drupal names to the native names for each database.
    *
-   * @return array
+   * @return string[]
    *   An array of Schema API field types to driver-specific field types.
    */
   abstract public function getFieldTypeMap();
diff --git a/core/lib/Drupal/Core/Database/StatementInterface.php b/core/lib/Drupal/Core/Database/StatementInterface.php
index 970612a..e2df75f 100644
--- a/core/lib/Drupal/Core/Database/StatementInterface.php
+++ b/core/lib/Drupal/Core/Database/StatementInterface.php
@@ -86,12 +86,12 @@ public function rowCount();
    *
    * @param int $mode
    *   One of the PDO::FETCH_* constants.
-   * @param int|string|object $a1
+   * @param int|string|object|null $a1
    *   An option depending of the fetch mode specified by $mode:
    *   - for PDO::FETCH_COLUMN, the index of the column to fetch
    *   - for PDO::FETCH_CLASS, the name of the class to create
    *   - for PDO::FETCH_INTO, the object to add the data to
-   * @param array $a2
+   * @param array|null $a2
    *   If $mode is PDO::FETCH_CLASS, the optional arguments to pass to the
    *   constructor.
    *