diff --git a/src/TraitExpressionBuilder.ts b/src/TraitExpressionBuilder.ts
index 94e6ff2..2885fe6 100644
--- a/src/TraitExpressionBuilder.ts
+++ b/src/TraitExpressionBuilder.ts
@@ -18,7 +18,7 @@ export class TraitExpressionBuilder<
 
 
     static spreadSupertraits<
-        const T extends Trait<
+        const T extends readonly Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
                 readonly Trait<any, any, any, any>[]
@@ -37,7 +37,7 @@ export class TraitExpressionBuilder<
     }
 
     static traitsUniq<
-        const T extends Trait<
+        const T extends readonly Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
                 readonly Trait<any, any, any, any>[]
@@ -65,7 +65,7 @@ export class TraitExpressionBuilder<
     }
 
     expresses<
-        const T extends Trait<
+        const T extends readonly Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
                 readonly Trait<any, any, any, any>[]
@@ -91,7 +91,7 @@ export class TraitExpressionBuilder<
     }
 
     expressesFirst<
-        const T extends Trait<
+        const T extends readonly Trait<
             TraitExpression<
                 typeof TraitExpression.NullSuperclass,
                 readonly Trait<any, any, any, any>[]