diff --git a/mailcheck/mailcheck.d.ts b/mailcheck/mailcheck.d.ts
index c6f28d0db..64b5f93c4 100644
--- a/mailcheck/mailcheck.d.ts
+++ b/mailcheck/mailcheck.d.ts
@@ -47,6 +47,7 @@ declare module MailcheckModule {
 
     export interface IOptions {
         domains?: string[];
+        secondLevelDomains?: string[];
         topLevelDomains?: string[];
         distanceFunction?: IDistanceFunction;
         suggested?: ISuggested | IJQuerySuggested;