diff --git a/src/serializers/index.ts b/src/serializers/index.ts
index a04b222..f76701f 100644
--- a/src/serializers/index.ts
+++ b/src/serializers/index.ts
@@ -28,7 +28,7 @@ export interface SerializerOptions {
    * Defaults to `DEFAULT_OMIT_HEADER_NAMES`,
    * and can be disabled by supplying an empty array `[]`.
    */
-  omitHeaderNames?: string[];
+  omitHeaderNames?: readonly string[];
 }
 
 interface Socket {
diff --git a/src/serializers/omitPropertiesSerializer.ts b/src/serializers/omitPropertiesSerializer.ts
index 5c4c7e2..a7bc734 100644
--- a/src/serializers/omitPropertiesSerializer.ts
+++ b/src/serializers/omitPropertiesSerializer.ts
@@ -5,7 +5,7 @@ export const createOmitPropertiesSerializer = (
   /**
    * A list of properties that should not be logged.
    */
-  properties: string[],
+  properties: readonly string[],
 ): SerializerFn => {
   const uniquePropertySet = new Set(properties);