diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 895409d..25e9b9a 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -2484,7 +2484,8 @@ function drupal_valid_test_ua($new_prefix = NULL) {
     // The file properties add more entropy not easily accessible to others.
     $key = drupal_get_hash_salt() . filectime(__FILE__) . fileinode(__FILE__);
     $time_diff = REQUEST_TIME - $time;
-    // We cant use Crypt::hmacBase64() yet.
+    // We cant use Crypt::hmacBase64() yet because this can be called in very
+    // early bootstrap when autoloader has not been initialized yet.
     $test_hmac = base64_encode(hash_hmac('sha256', $check_string, $key, TRUE));
     $test_hmac = strtr($test_hmac, array('+' => '-', '/' => '_', '=' => ''));
     // Since we are making a local request a 5 second time window is allowed,
diff --git a/core/lib/Drupal/Component/Utility/Crypt.php b/core/lib/Drupal/Component/Utility/Crypt.php
index d1e8db6..9fec8b5 100644
--- a/core/lib/Drupal/Component/Utility/Crypt.php
+++ b/core/lib/Drupal/Component/Utility/Crypt.php
@@ -74,12 +74,12 @@ public static function randomBytes($count) {
   /**
    * Calculates a base-64 encoded, URL-safe sha-256 hmac.
    *
-   * @param $data
+   * @param string $data
    *   String to be validated with the hmac.
-   * @param $key
+   * @param string $key
    *   A secret string key.
    *
-   * @return
+   * @return string
    *   A base-64 encoded sha-256 hmac, with + replaced with -, / with _ and
    *   any = padding characters removed.
    */
@@ -92,10 +92,10 @@ public static function hmacBase64($data, $key) {
   /**
    * Calculates a base-64 encoded, URL-safe sha-256 hash.
    *
-   * @param $data
+   * @param string $data
    *   String to be hashed.
    *
-   * @return
+   * @return string
    *   A base-64 encoded sha-256 hash, with + replaced with -, / with _ and
    *   any = padding characters removed.
    */
@@ -106,12 +106,12 @@ public static function hashBase64($data) {
   }
 
   /**
-   * Genearates a random, base-64 encoded, URL-safe, sha-256 hashed string.
+   * Generates a random, base-64 encoded, URL-safe, sha-256 hashed string.
    *
    * @param int $count
    *   The number of characters (bytes) of the string to be hashed.
    *
-   * @return
+   * @return string
    *   A base-64 encoded sha-256 hash, with + replaced with -, / with _ and
    *   any = padding characters removed.
    *
@@ -119,7 +119,7 @@ public static function hashBase64($data) {
    * @see \Drupal\Component\Utility\Crypt::hashBase64()
    */
   public static function randomStringHashed($count) {
-    return self::hashBase64(self::randomBytes($count));
+    return static::hashBase64(static::randomBytes($count));
   }
 
 }