2 files changed, 3 insertions, 2 deletions
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index 30e9e5634b..45075050eb 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -605,8 +605,9 @@ module ActionDispatch
         nil
       end
 
+      # The +options+ argument must be +nil+ or a hash whose keys are *symbols*.
       def url_for(options)
-        options = (options || {}).reverse_merge!(default_url_options)
+        options = default_url_options.merge(options || {})
 
         handle_positional_args(options)
 
diff --git a/actionpack/lib/action_dispatch/routing/url_for.rb b/actionpack/lib/action_dispatch/routing/url_for.rb
index bab501f27c..12ae2456d6 100644
--- a/actionpack/lib/action_dispatch/routing/url_for.rb
+++ b/actionpack/lib/action_dispatch/routing/url_for.rb
@@ -145,7 +145,7 @@ module ActionDispatch
       def url_for(options = nil)
         case options
         when nil
-          _routes.url_for(url_options)
+          _routes.url_for(url_options.symbolize_keys)
         when Hash
           symbolized = {}
           options.keys.each do |k|