diff --git a/src/expresses.ts b/src/expresses.ts
index fed933a..189b81e 100644
--- a/src/expresses.ts
+++ b/src/expresses.ts
@@ -1,6 +1,6 @@
-import { Fn, Pipe, Tuples } from "hotscript"
+import { Call, Fn, Pipe, Tuples } from "hotscript"
 import { AbstractClass, Opaque, Simplify } from "type-fest"
-import { Trait, TraitAbstractMembersFn, TraitApplierSuperTag } from "."
+import { Trait, TraitAbstractMembersFn, TraitApplierSuperTag, TraitImplInstanceFn } from "."
 import { ExtendFn } from "./util"
 
 
@@ -13,7 +13,16 @@ class TraitsExpression<
         readonly traits:      Traits,
     ) {}
 
-    extends() {
+    extends(): (
+        AbstractClass<
+            Call<ExtendFn, [
+                InstanceType<Super>,
+                ...Call<Tuples.Map<TraitImplInstanceFn>, Traits>,
+            ]>,
+
+            ConstructorParameters<Super>
+        >
+    ) {
         return this.traits.reduce(
             (previous, trait) => trait.apply(previous),
             this.superclass as Opaque<Super, TraitApplierSuperTag>,