diff --git a/phpseclib/Crypt/Salsa20.php b/phpseclib/Crypt/Salsa20.php
index 0a35f478..785e7aa2 100644
--- a/phpseclib/Crypt/Salsa20.php
+++ b/phpseclib/Crypt/Salsa20.php
@@ -326,7 +326,7 @@ class Salsa20 extends StreamCipher
             foreach ($blocks as &$block) {
                 $block ^= static::salsa20($this->p1 . pack('V', $i++) . $this->p2);
             }
-
+            unset($block);
             return implode('', $blocks);
         }
 
@@ -366,6 +366,7 @@ class Salsa20 extends StreamCipher
                     foreach ($blocks as &$block) {
                         $block ^= static::salsa20($this->p1 . pack('V', $buffer['counter']++) . $this->p2);
                     }
+                    unset($block);
                 }
                 $encrypted = implode('', $blocks);
                 $temp = static::salsa20($this->p1 . pack('V', $buffer['counter']++) . $this->p2);
@@ -388,6 +389,7 @@ class Salsa20 extends StreamCipher
                 foreach ($blocks as &$block) {
                     $block ^= static::salsa20($this->p1 . pack('V', $buffer['counter']++) . $this->p2);
                 }
+                unset($block);
                 $ciphertext .= implode('', $blocks);
             }
         }