diff --git a/README.md b/README.md
index daefa2f..8edaada 100644
--- a/README.md
+++ b/README.md
@@ -87,14 +87,12 @@ pluginBasicSsl({
 
 Options passing to `selfsigned`, see [selfsigned - Options](https://github.com/jfromaniello/selfsigned?tab=readme-ov-file#options) for details.
 
-In addition, the plugin supports a `days` option to set the validity period of the certificate. It is converted to `notAfterDate` and ignored if `notAfterDate` is set.
-
-- **Type:** `SelfsignedOptions & { days?: number }`
+- **Type:** `SelfsignedOptions`
 - **Default:**
 
 ```ts
 const defaultOptions = {
-  days: 30,
+  notAfterDate: new Date(Date.now() + 30 * 24 * 60 * 60 * 1000),
   keySize: 2048,
 };
 ```
@@ -104,7 +102,7 @@ const defaultOptions = {
 ```ts
 pluginBasicSsl({
   selfsignedOptions: {
-    days: 100,
+    notAfterDate: new Date(Date.now() + 100 * 24 * 60 * 60 * 1000),
   },
 });
 ```
diff --git a/src/index.ts b/src/index.ts
index 32d3264..dc17f97 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -22,14 +22,7 @@ export type PluginBasicSslOptions = {
   /**
    * Options passing to `selfsigned`.
    */
-  selfsignedOptions?: SelfsignedOptions & {
-    /**
-     * Validity period of the certificate in days.
-     * Ignored if `notAfterDate` is set.
-     * @default 30
-     */
-    days?: number;
-  };
+  selfsignedOptions?: SelfsignedOptions;
 };
 
 export const pluginBasicSsl = (
diff --git a/src/util.ts b/src/util.ts
index 8ae7f5e..e294f01 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -46,11 +46,10 @@ export const resolveHttpsConfig = async (
     options.filename ?? 'fake-cert.pem',
   );
 
-  const { days = 30, ...restOptions } = options.selfsignedOptions ?? {};
   const selfsignedOptions = {
     keySize: 2048,
-    notAfterDate: new Date(Date.now() + days * 24 * 60 * 60 * 1000),
-    ...restOptions,
+    notAfterDate: new Date(Date.now() + 30 * 24 * 60 * 60 * 1000),
+    ...options.selfsignedOptions,
   };
 
   if (fs.existsSync(certPath)) {
diff --git a/test/selfsigned-options/index.test.ts b/test/selfsigned-options/index.test.ts
index 84d2f21..8e9ddcb 100644
--- a/test/selfsigned-options/index.test.ts
+++ b/test/selfsigned-options/index.test.ts
@@ -13,7 +13,7 @@ test('should print HTTPS server URLs when custom selfsigned options', async () =
       plugins: [
         pluginBasicSsl({
           selfsignedOptions: {
-            days: 1,
+            notAfterDate: new Date(Date.now() + 24 * 60 * 60 * 1000),
           },
         }),
       ],