diff --git a/phpseclib/Math/PrimeField.php b/phpseclib/Math/PrimeField.php
index 6b85c724..7e15f906 100644
--- a/phpseclib/Math/PrimeField.php
+++ b/phpseclib/Math/PrimeField.php
@@ -111,4 +111,12 @@ class PrimeField extends FiniteField
     {
         return Integer::getModulo($this->instanceID)->getLength();
     }
+
+    /**
+     *  Destructor
+     */
+    public function __destruct()
+    {
+        Integer::cleanupCache($this->instanceID);
+    }
 }
\ No newline at end of file
diff --git a/phpseclib/Math/PrimeField/Integer.php b/phpseclib/Math/PrimeField/Integer.php
index c274ff64..c933f5c1 100644
--- a/phpseclib/Math/PrimeField/Integer.php
+++ b/phpseclib/Math/PrimeField/Integer.php
@@ -95,6 +95,15 @@ class Integer extends Base
         }
     }
 
+    /**
+     * Delete the modulo for a given instance
+     */
+    public static function cleanupCache($instanceID)
+    {
+        unset(static::$modulo[$instanceID]);
+        unset(static::$reduce[$instanceID]);
+    }
+
     /**
      * Returns the modulo
      *