diff --git a/README.md b/README.md
index de0d197..4e4637d 100644
--- a/README.md
+++ b/README.md
@@ -174,6 +174,9 @@ router.get('/:category/:title', function (ctx, next) {
 });
 ```
 
+The [path-to-regexp](https://github.com/pillarjs/path-to-regexp) module is used
+to convert paths to regular expressions.
+
 **Kind**: instance property of <code>[Router](#exp_module_koa-router--Router)</code>
 
 | Param | Type | Description |
diff --git a/lib/router.js b/lib/router.js
index 18de571..2b0b944 100644
--- a/lib/router.js
+++ b/lib/router.js
@@ -162,6 +162,9 @@ function Router(opts) {
  * });
  * ```
  *
+ * The [path-to-regexp](https://github.com/pillarjs/path-to-regexp) module is
+ * used to convert paths to regular expressions.
+ *
  * @name get|put|post|patch|delete
  * @memberof module:koa-router.prototype
  * @param {String} path