diff --git a/src/effect.ts b/src/effect.ts
index 4ef1242..53736ea 100644
--- a/src/effect.ts
+++ b/src/effect.ts
@@ -14,7 +14,7 @@ export function extendsEffectSchemaExpression<
     const Traits extends readonly Trait<any, any, any, any>[],
 >(
     expression: TraitExpression<
-        S.Class<void, Fields, A, I, R, C, Inherited, Proto>,
+        S.Class<unknown, Fields, A, I, R, C, Inherited, Proto>,
         Traits
     >
 ) {