diff --git a/phpseclib/Math/BigInteger.php b/phpseclib/Math/BigInteger.php
index bcc99e10..1c00b8a2 100644
--- a/phpseclib/Math/BigInteger.php
+++ b/phpseclib/Math/BigInteger.php
@@ -141,7 +141,6 @@ class BigInteger implements \Serializable
                 }
             }
         }
-
         if ($x instanceof self::$mainEngine) {
             $this->value = clone $x;
         } elseif ($x instanceof BigInteger\Engines\Engine) {
@@ -719,4 +718,4 @@ class BigInteger implements \Serializable
     {
         $this->value = clone $this->value;
     }
-}
\ No newline at end of file
+}
diff --git a/phpseclib/Math/BigInteger/Engines/Engine.php b/phpseclib/Math/BigInteger/Engines/Engine.php
index 3abdbc65..151f3b90 100644
--- a/phpseclib/Math/BigInteger/Engines/Engine.php
+++ b/phpseclib/Math/BigInteger/Engines/Engine.php
@@ -1036,4 +1036,4 @@ abstract class Engine implements \Serializable
         }
         return $max;
     }
-}
\ No newline at end of file
+}
diff --git a/phpseclib/Math/BigInteger/Engines/PHP.php b/phpseclib/Math/BigInteger/Engines/PHP.php
index feeeb65b..f437f2d6 100644
--- a/phpseclib/Math/BigInteger/Engines/PHP.php
+++ b/phpseclib/Math/BigInteger/Engines/PHP.php
@@ -70,13 +70,6 @@ abstract class PHP extends Engine
      * @access protected
      */
     const ENGINE_DIR = 'PHP';
-    
-    /**
-     * Primes > 2 and < 1000
-     *
-     * @var array
-     */
-    protected static $primes;
 
     /**
      * Default constructor
@@ -1279,7 +1272,7 @@ abstract class PHP extends Engine
         }
 
         $value = $this->value;
-        foreach (self::$primes as $prime) {
+        foreach (static::$primes as $prime) {
             list(, $r) = self::divide_digit($value, $prime);
             if (!$r) {
                 return count($value) == 1 && $value[0] == $prime;