3 files changed, 13 insertions, 1 deletions
diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 40f447ada7..a62f655dc2 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   In url_for, never append a question mark to the URL when the query string
+    is empty anyway.  (It used to do that when called like `url_for(controller:
+    'x', action: 'y', q: {})`.)
+
 *   Catch invalid UTF-8 querystring values and respond with BadRequest
 
     Check querystring params for invalid UTF-8 characters, and raise an
diff --git a/actionpack/lib/action_dispatch/http/url.rb b/actionpack/lib/action_dispatch/http/url.rb
index 92b10b6d3b..37f41ae988 100644
--- a/actionpack/lib/action_dispatch/http/url.rb
+++ b/actionpack/lib/action_dispatch/http/url.rb
@@ -81,7 +81,8 @@ module ActionDispatch
         def add_params(path, params)
           params = { params: params } unless params.is_a?(Hash)
           params.reject! { |_,v| v.to_param.nil? }
-          path << "?#{params.to_query}" unless params.empty?
+          query = params.to_query
+          path << "?#{query}" unless query.empty?
         end
 
         def add_anchor(path, anchor)
diff --git a/actionpack/test/dispatch/url_generation_test.rb b/actionpack/test/dispatch/url_generation_test.rb
index fd4ede4d1b..8c9782bb90 100644
--- a/actionpack/test/dispatch/url_generation_test.rb
+++ b/actionpack/test/dispatch/url_generation_test.rb
@@ -129,6 +129,13 @@ module TestUrlGeneration
       )
     end
 
+    test "generating URLS with empty querystring" do
+      assert_equal "/bars.json", bars_path(
+        a: {},
+        format: 'json'
+      )
+    end
+
   end
 end