diff --git a/src/Schema/MobX/ObservableClass.ts b/src/Schema/MobX/ObservableClass.ts
index 3be882a..61243c7 100644
--- a/src/Schema/MobX/ObservableClass.ts
+++ b/src/Schema/MobX/ObservableClass.ts
@@ -8,19 +8,19 @@ interface ObservableClassSelf {
     readonly fields: { readonly [K in keyof Schema.Struct.Fields]: Schema.Struct.Fields[K] }
 }
 
-export const ObservableClass = <Self extends ObservableClassSelf>(
-    self:      Self,
-    options?:  Omit<CreateObservableOptions, "proxy">,
-) =>
-    class Observable extends self {
-        declare ["constructor"]: typeof Observable
+interface ObservableClassOptions extends Omit<CreateObservableOptions, "proxy"> {}
 
-        constructor(...args: any[]) {
-            super(...args)
+export const ObservableClass = (options?: ObservableClassOptions) =>
+    <Self extends ObservableClassSelf>(self: Self) =>
+        class Observable extends self {
+            declare ["constructor"]: typeof Observable
 
-            makeObservable(this,
-                mapValues(this.constructor.fields, () => observable),
-                options,
-            )
-        }
-    } as Self
+            constructor(...args: any[]) {
+                super(...args)
+
+                makeObservable(this,
+                    mapValues(this.constructor.fields, () => observable),
+                    options,
+                )
+            }
+        } as Self
diff --git a/src/tests.ts b/src/tests.ts
index f1adbc7..de20458 100644
--- a/src/tests.ts
+++ b/src/tests.ts
@@ -1,5 +1,5 @@
 import { Schema as S } from "@effect/schema"
-import { reaction, runInAction } from "mobx"
+import { computed, makeObservable, reaction, runInAction } from "mobx"
 import type { Simplify } from "type-fest"
 import { MutableTaggedClass, toJsonifiable } from "./Schema"
 import { ObservableClass } from "./Schema/MobX"
@@ -18,12 +18,24 @@ type TestB = {
 type Merged = Simplify<ExtendAll<[TestA, TestB]>>
 
 
-class User extends MutableTaggedClass<User>()("User", {
+
+const UserSchema = MutableTaggedClass<User>()("User", {
     id:    S.BigIntFromSelf,
     role:  S.Union(S.Literal("BasicUser"), S.Literal("Admin")),
 }).pipe(
-    ObservableClass
-) {}
+    ObservableClass()
+)
+
+class User extends UserSchema {
+    constructor(...args: ConstructorParameters<typeof UserSchema>) {
+        super(...args)
+        makeObservable(this, { idAsString: computed })
+    }
+
+    get idAsString() {
+        return this.id.toString()
+    }
+}
 
 const JsonifiableUser = User.pipe(
     toJsonifiable(S.Struct({