diff --git a/src/TraitExpression.ts b/src/TraitExpression.ts
index c0ea010..a20ca73 100644
--- a/src/TraitExpression.ts
+++ b/src/TraitExpression.ts
@@ -63,10 +63,12 @@ export class TraitExpression<
 export const emptyTraitExpression = new TraitExpression(TraitExpressionNullSuperclass, [] as const)
 
 interface PrependTraitSupertraitsFn extends Fn {
-    return: [
-        ...Call<TraitSupertraitsFn, this["arg0"]>,
-        this["arg0"],
-    ]
+    return: this["arg0"] extends Trait<any, any, any>
+        ? [
+            ...Call<TraitSupertraitsFn, this["arg0"]>,
+            this["arg0"],
+        ]
+        : never
 }
 export interface TraitExpressionTraitsFn extends Fn {
     return: this["arg0"] extends TraitExpression<any, infer Traits>
diff --git a/src/tests.ts b/src/tests.ts
index 710a660..421b746 100644
--- a/src/tests.ts
+++ b/src/tests.ts
@@ -1,4 +1,5 @@
-import { Implements, abstract, expression, trait } from "."
+import { Call } from "hotscript"
+import { Implements, TraitExpressionTraitsFn, abstract, expression, trait } from "."
 
 
 const PrintsHelloOnNew = trait(
@@ -54,10 +55,11 @@ const builder = expression
         PrintsHelloOnNew,
         Identifiable<bigint>(),
         // Identifiable<number>(),
+        StatefulSubscription,
     )
 
 const exp = builder.get()
-type Abs = Implements<typeof exp>
+type Abs = Call<TraitExpressionTraitsFn, typeof exp>
 
 class User extends exp.extends implements Implements<typeof exp> {
     id: bigint = -1n