diff --git a/cloudtrail-key/main.tf b/cloudtrail-key/main.tf
index 0f9bf43..a76b2af 100644
--- a/cloudtrail-key/main.tf
+++ b/cloudtrail-key/main.tf
@@ -58,7 +58,7 @@ locals {
   kms_key_name        = format("k-%v", local.name)
   kms_admin_root      = format("arn:%v:iam::%v:root", local.partition, local.account_id)
   kms_admin_roles     = compact(concat([local.kms_admin_root], var.kms_admin_roles))
-  kms_policy_document = length(var.kms_policy_document) > 0 ? var.kms_policy_document : data.aws_iam_policy_document.empty.json
+  kms_policy_document = var.kms_policy_document != null ? var.kms_policy_document : data.aws_iam_policy_document.empty.json
 
 }