diff --git a/src/Trait.ts b/src/Trait.ts
index 9d43662..63109a6 100644
--- a/src/Trait.ts
+++ b/src/Trait.ts
@@ -6,7 +6,7 @@ import { Extend, StaticMembers } from "./util"
 export class Trait<
     SuperExpression extends TraitExpression<
         typeof TraitExpression.NullSuperclass,
-        Trait<any, any, any, any>[]
+        readonly Trait<any, any, any, any>[]
     >,
     Abstract        extends object,
     StaticAbstract  extends object,
diff --git a/src/TraitBuilder.ts b/src/TraitBuilder.ts
index b0e4f3c..abe27ae 100644
--- a/src/TraitBuilder.ts
+++ b/src/TraitBuilder.ts
@@ -10,7 +10,7 @@ declare const implSuperSymbol: unique symbol
 export class TraitBuilder<
     SuperExpression extends TraitExpression<
         typeof TraitExpression.NullSuperclass,
-        Trait<any, any, any, any>[]
+        readonly Trait<any, any, any, any>[]
     >,
     Abstract        extends object,
     StaticAbstract  extends object,
diff --git a/src/TraitExpression.ts b/src/TraitExpression.ts
index 62b3624..44367d0 100644
--- a/src/TraitExpression.ts
+++ b/src/TraitExpression.ts
@@ -6,7 +6,7 @@ import { Extend, StaticMembers } from "./util"
 
 export class TraitExpression<
     Superclass   extends AbstractClass<object>,
-    const Traits extends Trait<any, any, any, any>[],
+    const Traits extends readonly Trait<any, any, any, any>[],
 > {
     constructor(
         readonly superclass:  Superclass,
@@ -95,7 +95,7 @@ export namespace TraitExpression {
 
 
 export type Implements<
-    Exp extends TraitExpression<any, Trait<any, any, any, any>[]>
+    Exp extends TraitExpression<any, readonly Trait<any, any, any, any>[]>
 > = (
     Simplify<
         Extend<
@@ -107,7 +107,7 @@ export type Implements<
 )
 
 export type StaticImplements<
-    Exp extends TraitExpression<any, Trait<any, any, any, any>[]>
+    Exp extends TraitExpression<any, readonly Trait<any, any, any, any>[]>
 > = (
     Simplify<
         Extend<
@@ -120,7 +120,7 @@ export type StaticImplements<
 
 
 export type TraitExpressionClass<
-    Exp extends TraitExpression<any, Trait<any, any, any, any>[]>
+    Exp extends TraitExpression<any, readonly Trait<any, any, any, any>[]>
 > = (
     AbstractClass<
         TraitExpressionInstance<Exp>,
@@ -130,7 +130,7 @@ export type TraitExpressionClass<
 )
 
 export type TraitExpressionConcreteClass<
-    Exp extends TraitExpression<any, Trait<any, any, any, any>[]>
+    Exp extends TraitExpression<any, readonly Trait<any, any, any, any>[]>
 > = (
     Class<
         TraitExpressionInstance<Exp>,
@@ -140,7 +140,7 @@ export type TraitExpressionConcreteClass<
 )
 
 export type TraitExpressionInstance<
-    Exp extends TraitExpression<any, Trait<any, any, any, any>[]>
+    Exp extends TraitExpression<any, readonly Trait<any, any, any, any>[]>
 > = (
     InstanceType<TraitExpression.Superclass<Exp>> &  // Keep the instance of the superclass outside of any kind of type manipulation
                                                      // as it can accidentely remove abstract properties
@@ -152,7 +152,7 @@ export type TraitExpressionInstance<
 )
 
 export type TraitExpressionStaticMembers<
-    Exp extends TraitExpression<any, Trait<any, any, any, any>[]>
+    Exp extends TraitExpression<any, readonly Trait<any, any, any, any>[]>
 > = (
     Simplify<
         Extend<[
diff --git a/src/TraitExpressionBuilder.ts b/src/TraitExpressionBuilder.ts
index aa9acec..94e6ff2 100644
--- a/src/TraitExpressionBuilder.ts
+++ b/src/TraitExpressionBuilder.ts
@@ -7,7 +7,7 @@ import { Extendable, StaticMembers } from "./util"
 
 export class TraitExpressionBuilder<
     Superclass   extends AbstractClass<object>,
-    const Traits extends Trait<any, any, any, any>[],
+    const Traits extends readonly Trait<any, any, any, any>[],
 > {
     declare ["constructor"]: typeof TraitExpressionBuilder
 
@@ -21,7 +21,7 @@ export class TraitExpressionBuilder<
         const T extends Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
-                Trait<any, any, any, any>[]
+                readonly Trait<any, any, any, any>[]
             >,
             any,
             any,
@@ -40,7 +40,7 @@ export class TraitExpressionBuilder<
         const T extends Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
-                Trait<any, any, any, any>[]
+                readonly Trait<any, any, any, any>[]
             >,
             any,
             any,
@@ -68,7 +68,7 @@ export class TraitExpressionBuilder<
         const T extends Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
-                Trait<any, any, any, any>[]
+                readonly Trait<any, any, any, any>[]
             >,
             any,
             any,
@@ -94,7 +94,7 @@ export class TraitExpressionBuilder<
         const T extends Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
-                Trait<any, any, any, any>[]
+                readonly Trait<any, any, any, any>[]
             >,
             any,
             any,
@@ -194,7 +194,7 @@ export namespace TraitExpressionBuilder {
 
     export type BuildTraitExpression<
         Superclass extends AbstractClass<object>,
-        Traits     extends Trait<any, any, any, any>[],
+        Traits     extends readonly Trait<any, any, any, any>[],
     > = (
         Extendable<TraitTuple.MapAbstract<Traits>> extends false
             ? "Type conflict between the traits abstract definitions."