diff --git a/src/effect/schema/class/MobXObservable.ts b/src/effect/schema/class/MobXObservable.ts
index 5ebbeb8..bf7b08c 100644
--- a/src/effect/schema/class/MobXObservable.ts
+++ b/src/effect/schema/class/MobXObservable.ts
@@ -1,13 +1,15 @@
 import type { Struct } from "@effect/schema/Schema"
 import { makeObservable, observable, type CreateObservableOptions } from "mobx"
 import { mapValues } from "remeda"
-import type { Constructor } from "type-fest"
 
 
+interface MobXObservableInput {
+    new(...args: any[]): Struct.Type<Struct.Fields>
+    readonly fields: { readonly [K in keyof Struct.Fields]: Struct.Fields[K] }
+}
+
 export function MobXObservable<
-    This extends Constructor<Struct.Type<Struct.Fields>, any> & {
-        readonly fields: { readonly [K in keyof Struct.Fields]: Struct.Fields[K] }
-    }
+    This extends MobXObservableInput
 >(
     class_:    This,
     options?:  Omit<CreateObservableOptions, "proxy">,