diff --git a/index.js b/index.js
index 21297bc..97002bf 100644
--- a/index.js
+++ b/index.js
@@ -115,7 +115,7 @@ Router.prototype.on = function on (method, path, opts, handler, store) {
     assert(path.length === optionalParamMatch.index + optionalParamMatch[0].length, 'Optional Parameter needs to be the last parameter of the path')
 
     const pathFull = path.replace(OPTIONAL_PARAM_REGEXP, '$1$2')
-    const pathOptional = path.replace(OPTIONAL_PARAM_REGEXP, '$2')
+    const pathOptional = path.replace(OPTIONAL_PARAM_REGEXP, '$2') || '/'
 
     this.on(method, pathFull, opts, handler, store)
     this.on(method, pathOptional, opts, handler, store)
diff --git a/test/optional-params.test.js b/test/optional-params.test.js
index 2d9c8eb..c1534ba 100644
--- a/test/optional-params.test.js
+++ b/test/optional-params.test.js
@@ -195,3 +195,23 @@ test('deregister a route with optional param', (t) => {
   t.notOk(findMyWay.find('GET', '/a/:param/b'))
   t.notOk(findMyWay.find('GET', '/a/:param/b/:optional'))
 })
+
+test('optional parameter on root', (t) => {
+  t.plan(2)
+  const findMyWay = FindMyWay({
+    defaultRoute: (req, res) => {
+      t.fail('Should not be defaultRoute')
+    }
+  })
+
+  findMyWay.on('GET', '/:optional?', (req, res, params) => {
+    if (params.optional) {
+      t.equal(params.optional, 'foo')
+    } else {
+      t.equal(params.optional, undefined)
+    }
+  })
+
+  findMyWay.lookup({ method: 'GET', url: '/', headers: {} }, null)
+  findMyWay.lookup({ method: 'GET', url: '/foo', headers: {} }, null)
+})