diff --git a/types/helmet/helmet-tests.ts b/types/helmet/helmet-tests.ts
index 8b4c5634ac..f73095b714 100644
--- a/types/helmet/helmet-tests.ts
+++ b/types/helmet/helmet-tests.ts
@@ -122,13 +122,13 @@ function hpkpTest() {
     app.use(helmet.hpkp({
         maxAge: 7776000000,
         sha256s: ['AbCdEf123=', 'ZyXwVu456='],
-        includeSubdomains: false
+        includeSubDomains: false
     }));
 
     app.use(helmet.hpkp({
         maxAge: 7776000000,
         sha256s: ['AbCdEf123=', 'ZyXwVu456='],
-        includeSubdomains: true
+        includeSubDomains: true
     }));
 
     app.use(helmet.hpkp({
@@ -164,7 +164,7 @@ function hstsTest() {
 
     app.use(helmet.hsts({
       maxAge: 7776000000,
-      includeSubdomains: true
+      includeSubDomains: true
     }));
 
     app.use(helmet.hsts({
diff --git a/types/helmet/index.d.ts b/types/helmet/index.d.ts
index 565dda9ebf..573395831b 100644
--- a/types/helmet/index.d.ts
+++ b/types/helmet/index.d.ts
@@ -142,7 +142,7 @@ declare namespace helmet {
 
     export interface IHelmetHstsConfiguration {
         maxAge?: number;
-        includeSubdomains?: boolean;
+        includeSubDomains?: boolean;
         preload?: boolean;
         setIf?: IHelmetSetIfFunction;
         force?: boolean;