diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index b5c30432cdba987381973a146b8a27ac29592ffd..63c1b0d6366bd761f42fb0417d39210dcfa70e57 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -398,12 +398,21 @@ def dispatcher(raise_on_name_error)
           end
       end
 
-      # Invokes Journey::Router::Utils.normalize_path and ensure that
-      # (:locale) becomes (/:locale) instead of /(:locale). Except
-      # for root cases, where the latter is the correct one.
+      # Invokes Journey::Router::Utils.normalize_path, then ensures that
+      # /(:locale) becomes (/:locale). Except for root cases, where the
+      # former is the correct one.
       def self.normalize_path(path)
         path = Journey::Router::Utils.normalize_path(path)
-        path.gsub!(%r{/(\(+)/?}, '\1/') unless %r{^/(\(+[^)]+\)){1,}$}.match?(path)
+
+        # the path for a root URL at this point can be something like
+        # "/(/:locale)(/:platform)/(:browser)", and we would want
+        # "/(:locale)(/:platform)(/:browser)"
+
+        # reverse "/(", "/((" etc to "(/", "((/" etc
+        path.gsub!(%r{/(\(+)/?}, '\1/')
+        # if a path is all optional segments, change the leading "(/" back to
+        # "/(" so it evaluates to "/" when interpreted with no options.
+        path.sub!(%r{^(\(+)/}, '/\1') if %r{^(\(+[^)]+\)){1,}$}.match?(path)
         path
       end
 
diff --git a/actionpack/test/dispatch/routing_test.rb b/actionpack/test/dispatch/routing_test.rb
index ce3f32d950232a6ede4e9395c4d4da92e0f2ac00..e3d537d84dc7b066cf5971348ee229d3e6c8de1a 100644
--- a/actionpack/test/dispatch/routing_test.rb
+++ b/actionpack/test/dispatch/routing_test.rb
@@ -1382,7 +1382,7 @@ def test_scoped_root_as_name
     assert_equal "projects#index", @response.body
   end
 
-  def test_optionally_scoped_root_unscoped_access
+  def test_optional_scoped_root_hierarchy
     draw do
       scope "(:locale)" do
         scope "(:platform)" do
@@ -1394,8 +1394,22 @@ def test_optionally_scoped_root_unscoped_access
     end
 
     assert_equal "/", root_path
+    assert_equal "/en", root_path(locale: "en")
+    assert_equal "/en/osx", root_path(locale: "en", platform: "osx")
+    assert_equal "/en/osx/chrome",
+      root_path(locale: "en", platform: "osx", browser: "chrome")
+
     get "/"
     assert_equal "projects#index", @response.body
+
+    get "/en"
+    assert_equal "projects#index", @response.body
+
+    get "/en/osx"
+    assert_equal "projects#index", @response.body
+
+    get "/en/osx/chrome"
+    assert_equal "projects#index", @response.body
   end
 
   def test_scope_with_format_option