diff --git a/index.d.ts b/index.d.ts
index 8a920c8..6489eb8 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,7 +1,7 @@
-export declare namespace Base {
-  type Options = {
+export namespace Base {
+  interface Options {
     [key: string]: unknown;
-  };
+  }
 }
 
 declare type ApiExtension = {
diff --git a/index.test-d.ts b/index.test-d.ts
index f8fcddc..dc522d0 100644
--- a/index.test-d.ts
+++ b/index.test-d.ts
@@ -4,6 +4,7 @@ import { Base } from "./index.js";
 import { fooPlugin } from "./plugins/foo/index.js";
 import { barPlugin } from "./plugins/bar/index.js";
 import { voidPlugin } from "./plugins/void/index.js";
+import { withOptionsPlugin } from "./plugins/with-options";
 
 const base = new Base();
 
@@ -48,3 +49,8 @@ expectType<string>(baseWithVoidAndNonVoidPlugins.bar);
 
 // @ts-expect-error unknown properties cannot be used, see #31
 baseWithVoidAndNonVoidPlugins.unknown;
+
+const BaseWithOptionsPlugin = Base.plugin(withOptionsPlugin);
+const baseWithOptionsPlugin = new BaseWithOptionsPlugin();
+
+expectType<string>(baseWithOptionsPlugin.getFooOption());
diff --git a/plugins/with-options/index.d.ts b/plugins/with-options/index.d.ts
new file mode 100644
index 0000000..7d97f99
--- /dev/null
+++ b/plugins/with-options/index.d.ts
@@ -0,0 +1,17 @@
+// https://www.typescriptlang.org/docs/handbook/declaration-files/templates/module-plugin-d-ts.html
+import { Base } from "../..";
+
+declare module "../.." {
+  namespace Base {
+    interface Options {
+      foo?: string;
+    }
+  }
+}
+
+export function withOptionsPlugin(
+  base: Base,
+  options: Base.Options
+): {
+  getFooOption: () => Required<Base.Options>["foo"];
+};
diff --git a/plugins/with-options/index.js b/plugins/with-options/index.js
new file mode 100644
index 0000000..7decc7d
--- /dev/null
+++ b/plugins/with-options/index.js
@@ -0,0 +1,11 @@
+/**
+ * @param {import('../..').Base} base
+ * @param {import('../..').Base.Options} options
+ */
+export function withOptionsPlugin(base, options) {
+  return {
+    getFooOption() {
+      return options.foo || "my default";
+    },
+  };
+}