diff --git a/lib/rsa.js b/lib/rsa.js
index f3b32021..86a7557e 100644
--- a/lib/rsa.js
+++ b/lib/rsa.js
@@ -286,6 +286,7 @@ var digestInfoValidator = {
       name: 'DigestInfo.DigestAlgorithm.parameters',
       tagClass: asn1.Class.UNIVERSAL,
       type: asn1.Type.NULL,
+      optional: true,
       constructed: false
     }]
   }, {