3 files changed, 25 insertions, 0 deletions
diff --git a/actionpack/lib/action_dispatch/http/parameters.rb b/actionpack/lib/action_dispatch/http/parameters.rb
index d9b63faf5e..bcfd0b0d00 100644
--- a/actionpack/lib/action_dispatch/http/parameters.rb
+++ b/actionpack/lib/action_dispatch/http/parameters.rb
@@ -35,6 +35,10 @@ module ActionDispatch
         @env["action_dispatch.request.path_parameters"] ||= {}
       end
 
+      def reset_parameters #:nodoc:
+        @env.delete("action_dispatch.request.parameters")
+      end
+
     private
 
       # TODO: Validate that the characters are UTF-8. If they aren't,
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index 1a1a054985..4ea3937057 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -35,6 +35,8 @@ module ActionDispatch
           }
 
           return true
+        ensure
+          req.reset_parameters
         end
 
         def call(env)
diff --git a/actionpack/test/dispatch/routing_test.rb b/actionpack/test/dispatch/routing_test.rb
index 4b8d308043..a96d2edcf9 100644
--- a/actionpack/test/dispatch/routing_test.rb
+++ b/actionpack/test/dispatch/routing_test.rb
@@ -2512,3 +2512,22 @@ private
     %(<html><body>You are being <a href="#{ERB::Util.h(url)}">redirected</a>.</body></html>)
   end
 end
+
+class TestConstraintsAccessingParameters < ActionDispatch::IntegrationTest
+  Routes = ActionDispatch::Routing::RouteSet.new.tap do |app|
+    app.draw do
+      ok = lambda { |env| [200, { 'Content-Type' => 'text/plain' }, []] }
+
+      get "/:foo" => ok, :constraints => lambda { |r| r.params[:foo] == 'foo' }
+      get "/:bar" => ok
+    end
+  end
+
+  def app; Routes end
+
+  test "parameters are reset between constraint checks" do
+    get "/bar"
+    assert_equal nil, @request.params[:foo]
+    assert_equal "bar", @request.params[:bar]
+  end
+end