diff --git a/Crypto/SMimeSigner.php b/Crypto/SMimeSigner.php
index 243aaf1..1b55537 100644
--- a/Crypto/SMimeSigner.php
+++ b/Crypto/SMimeSigner.php
@@ -24,11 +24,6 @@ final class SMimeSigner extends SMime
     private $signOptions;
     private $extraCerts;
 
-    /**
-     * @var string|null
-     */
-    private $privateKeyPassphrase;
-
     /**
      * @param string      $certificate          The path of the file containing the signing certificate (in PEM format)
      * @param string      $privateKey           The path of the file containing the private key (in PEM format)
@@ -52,7 +47,6 @@ public function __construct(string $certificate, string $privateKey, string $pri
 
         $this->signOptions = $signOptions ?? PKCS7_DETACHED;
         $this->extraCerts = $extraCerts ? realpath($extraCerts) : null;
-        $this->privateKeyPassphrase = $privateKeyPassphrase;
     }
 
     public function sign(Message $message): Message