diff --git a/types/webappsec-credential-management/index.d.ts b/types/webappsec-credential-management/index.d.ts
index 4c47ee7cc8..c8fbf8ec60 100644
--- a/types/webappsec-credential-management/index.d.ts
+++ b/types/webappsec-credential-management/index.d.ts
@@ -1,6 +1,7 @@
 // Type definitions for W3C (WebAppSec) Credential Management API Level 1, 0.3
 // Project: https://github.com/w3c/webappsec-credential-management
 // Definitions by: Iain McGinniss <https://github.com/iainmcgin>
+//                 Joao Peixoto <https://github.com/Hartimer>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.7
 
@@ -493,7 +494,7 @@ interface AuthenticatorAttestationResponse extends AuthenticatorResponse {
 interface AuthenticatorAssertionResponse extends AuthenticatorResponse {
     readonly authenticatorData: ArrayBuffer;
     readonly signature: ArrayBuffer;
-    readonly userHandle: ArrayBuffer;
+    readonly userHandle?: ArrayBuffer;
 }
 
 /**
diff --git a/types/webappsec-credential-management/webappsec-credential-management-tests.ts b/types/webappsec-credential-management/webappsec-credential-management-tests.ts
index 2afa9f8785..1e0500dfce 100644
--- a/types/webappsec-credential-management/webappsec-credential-management-tests.ts
+++ b/types/webappsec-credential-management/webappsec-credential-management-tests.ts
@@ -352,3 +352,16 @@ function webauthnAuthenticate() {
         console.log(e.message);
     });
 }
+
+function mockAuthenticatorAssertionResponse() {
+    if (!navigator.credentials) {
+        return;
+    }
+
+    const sampleResponse: AuthenticatorAssertionResponse = {
+        clientDataJSON: new ArrayBuffer(0),
+        authenticatorData: new ArrayBuffer(0),
+        signature: new ArrayBuffer(0),
+    };
+    sampleResponse.userHandle === undefined;
+}