diff --git a/src/traits/MobXObservableZodSchemaObject.ts b/src/traits/MobXObservableZodSchemaObject.ts
index 110cb91..c9913da 100644
--- a/src/traits/MobXObservableZodSchemaObject.ts
+++ b/src/traits/MobXObservableZodSchemaObject.ts
@@ -13,7 +13,10 @@ export const MobXObservableZodSchemaObject = trait
             super(...args)
 
             makeObservable(this,
-                mapValues(ObservableZodSchemaObject.schema.shape, () => observable)
+                mapValues(
+                    (this.constructor as typeof ObservableZodSchemaObject).schema.shape,
+                    () => observable,
+                )
             )
         }
     })