diff --git a/core/modules/system/src/SystemRequirements.php b/core/modules/system/src/SystemRequirements.php
index a0da2f2..17a821f 100644
--- a/core/modules/system/src/SystemRequirements.php
+++ b/core/modules/system/src/SystemRequirements.php
@@ -16,19 +16,19 @@ class SystemRequirements {
    * The minimum PHP version in the lower range for the introduction
    * of PDO::MYSQL_ATTR_MULTI_STATEMENTS.
    */
-  public static $minLow = '5.5.21';
+  const MIN_LOW = '5.5.21';
 
   /**
    * The maximum PHP version in the lower range for the introduction
    * of PDO::MYSQL_ATTR_MULTI_STATEMENTS.
    */
-  public static $maxLow = '5.6.0';
+  const MAX_LOW = '5.6.0';
 
   /**
    * The minimum PHP version in the higher range for the introduction
    * of PDO::MYSQL_ATTR_MULTI_STATEMENTS.
    */
-  public static $minHigh = '5.6.5';
+  const MIN_HIGH = '5.6.5';
 
   /**
    * Determines whether the passed in PHP version disallows multiple statements.
@@ -38,8 +38,8 @@ class SystemRequirements {
    * @return bool
    */
   public static function phpVersionWithPdoDisallowMultipleStatements($phpversion) {
-    return (version_compare($phpversion, self::$minLow, '>=') && version_compare($phpversion, self::$maxLow, '<'))
-      || version_compare($phpversion, self::$minHigh, '>=');
+    return (version_compare($phpversion, self::MIN_LOW, '>=') && version_compare($phpversion, self::MAX_LOW, '<'))
+      || version_compare($phpversion, self::MIN_HIGH, '>=');
   }
 
 }
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index ef0f615..392fbd9 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -87,7 +87,7 @@ function system_requirements($phase) {
   }
   elseif (($phase === 'install' || \Drupal::database()->driver() === 'mysql') && !SystemRequirements::phpVersionWithPdoDisallowMultipleStatements($phpversion)) {
     $requirements['php']['title'] = t('PHP (multiple statement disabling)');
-    $requirements['php']['description'] = t('PHP versions higher than %min_low or %min_high provide built-in SQL injection protection for mysql databases. It is recommended to update.', array('%min_low' => SystemRequirements::$minLow, '%min_high' => SystemRequirements::$minHigh));
+    $requirements['php']['description'] = t('PHP versions higher than %min_low or %min_high provide built-in SQL injection protection for mysql databases. It is recommended to update.', array('%min_low' => SystemRequirements::MIN_LOW, '%min_high' => SystemRequirements::MIN_HIGH));
     $requirements['php']['severity'] = REQUIREMENT_INFO;
   }
   elseif (version_compare($phpversion, DRUPAL_SUGGESTED_PHP) < 0) {