diff --git a/lib/types/request.d.ts b/lib/types/request.d.ts
index 969f6a19f..078fc3c95 100644
--- a/lib/types/request.d.ts
+++ b/lib/types/request.d.ts
@@ -307,7 +307,7 @@ export type MergeType<T, U> = {
     [K in keyof T]: K extends keyof U
         ? U[K]
         : T[K];
-} & U;
+};
 
 export type MergeRefs<T extends ReqRef> = MergeType<ReqRefDefaults, T>;
 
diff --git a/lib/types/response.d.ts b/lib/types/response.d.ts
index 0489e3fae..f7c131787 100644
--- a/lib/types/response.d.ts
+++ b/lib/types/response.d.ts
@@ -6,7 +6,6 @@ import {
     UserCredentials,
     AppCredentials,
     AuthArtifacts,
-    MergeType,
     AuthCredentials,
     ReqRef,
     ReqRefDefaults,
@@ -391,7 +390,7 @@ export interface AuthenticationData<
     CredentialsExtra = Record<string, unknown>,
     ArtifactsExtra = AuthArtifacts
 > {
-    credentials: MergeType<CredentialsExtra, AuthCredentials<AuthUser, AuthApp>>;
+    credentials: AuthCredentials<AuthUser, AuthApp> & CredentialsExtra;
     artifacts?: ArtifactsExtra | undefined;
 }