diff --git a/lib/Horde/Crypt/Smime.php b/lib/Horde/Crypt/Smime.php
index 8f5d7a8..03576c5 100644
--- a/lib/Horde/Crypt/Smime.php
+++ b/lib/Horde/Crypt/Smime.php
@@ -50,7 +50,7 @@ public function verifyPassphrase($private_key, $passphrase)
             ? openssl_pkey_get_private($private_key)
             : openssl_pkey_get_private($private_key, $passphrase);
 
-        return is_resource($res);
+        return boolval($res);
     }
 
     /**