diff --git a/src/effect/schema/class/Mutable.ts b/src/effect/schema/class/Mutable.ts
index 78bbe1e..78569eb 100644
--- a/src/effect/schema/class/Mutable.ts
+++ b/src/effect/schema/class/Mutable.ts
@@ -39,17 +39,18 @@ extends Omit<
 }
 
 
-type MutableInput<
+interface MutableInput<
     Self,
     Fields extends Schema.Struct.Fields,
     I, R, C,
     Inherited,
     Proto
-> = Omit<Schema.Class<Self, Fields, I, R, C, Inherited, Proto>,
-    | "extend"
-    | "transformOrFail"
-    | "transformOrFailFrom"
->
+> extends StaticType<Schema.Class<Self, Fields, I, R, C, Inherited, Proto>> {
+    new(
+        props: any,
+        options?: any,
+      ): Schema.Struct.Type<Fields> & Omit<Inherited, keyof Fields> & Proto
+}
 
 export const Mutable = <
     Self,
diff --git a/src/effect/schema/tests.ts b/src/effect/schema/tests.ts
index d2fa624..86360b1 100644
--- a/src/effect/schema/tests.ts
+++ b/src/effect/schema/tests.ts
@@ -12,12 +12,14 @@ import { Mutable } from "./class/Mutable"
 //     MobXObservable
 // ) {}
 
-class User extends Class<User>("User")({
+const UserProto = Class<User>("User")({
     id:    S.BigIntFromSelf,
     role:  S.Union(S.Literal("BasicUser"), S.Literal("Admin")),
-}) {}
+})
 
-const MutableUser = Mutable(User)
+class User extends UserProto {}
+
+const MutableUser = Mutable(UserProto)
 
 const JsonifiableUser = User.pipe(
     Jsonifiable(S.Struct({