diff --git a/src/Trait.ts b/src/Trait.ts
index 63109a6..d2f1f2e 100644
--- a/src/Trait.ts
+++ b/src/Trait.ts
@@ -74,43 +74,43 @@ export namespace Trait {
 
 export namespace TraitTuple {
     export type MapAbstract<T> = {
-        [K in keyof T]: K extends keyof []
+        [K in keyof T]: K extends keyof readonly []
             ? T[K]
             : Trait.Abstract<T[K]>
     }
 
     export type MapStaticAbstract<T> = {
-        [K in keyof T]: K extends keyof []
+        [K in keyof T]: K extends keyof readonly []
             ? T[K]
             : Trait.StaticAbstract<T[K]>
     }
 
     export type MapImplClass<T> = {
-        [K in keyof T]: K extends keyof []
+        [K in keyof T]: K extends keyof readonly []
             ? T[K]
             : Trait.ImplClass<T[K]>
     }
 
     export type MapImplInstance<T> = {
-        [K in keyof T]: K extends keyof []
+        [K in keyof T]: K extends keyof readonly []
             ? T[K]
             : Trait.ImplInstance<T[K]>
     }
 
     export type MapImplStaticMembers<T> = {
-        [K in keyof T]: K extends keyof []
+        [K in keyof T]: K extends keyof readonly []
             ? T[K]
             : Trait.ImplStaticMembers<T[K]>
     }
 
     export type MapInstance<T> = {
-        [K in keyof T]: K extends keyof []
+        [K in keyof T]: K extends keyof readonly []
             ? T[K]
             : Trait.Instance<T[K]>
     }
 
     export type MapStaticMembers<T> = {
-        [K in keyof T]: K extends keyof []
+        [K in keyof T]: K extends keyof readonly []
             ? T[K]
             : Trait.Static<T[K]>
     }
diff --git a/src/TraitExpressionBuilder.ts b/src/TraitExpressionBuilder.ts
index 3591c74..60335c9 100644
--- a/src/TraitExpressionBuilder.ts
+++ b/src/TraitExpressionBuilder.ts
@@ -176,7 +176,7 @@ export namespace TraitExpressionBuilder {
         Traits extends readonly Trait<any, any, any, any>[],
         T      extends readonly Trait<any, any, any, any>[],
     > = (
-        TraitExpressionBuilder.TraitsUniq<[
+        TraitExpressionBuilder.TraitsUniq<readonly [
             ...Traits,
             ...TraitExpressionBuilder.SpreadSupertraits<T>,
         ]>
@@ -186,7 +186,7 @@ export namespace TraitExpressionBuilder {
         Traits extends readonly Trait<any, any, any, any>[],
         T      extends readonly Trait<any, any, any, any>[],
     > = (
-        TraitExpressionBuilder.TraitsUniq<[
+        TraitExpressionBuilder.TraitsUniq<readonly [
             ...TraitExpressionBuilder.SpreadSupertraits<T>,
             ...Traits,
         ]>