1 files changed, 4 insertions, 2 deletions
diff --git a/actionpack/lib/action_controller/renderer.rb b/actionpack/lib/action_controller/renderer.rb
index 0739f16965..3ff80e6a39 100644
--- a/actionpack/lib/action_controller/renderer.rb
+++ b/actionpack/lib/action_controller/renderer.rb
@@ -83,7 +83,7 @@ module ActionController
     private
       def normalize_keys(env)
         new_env = {}
-        env.each_pair { |k,v| new_env[rack_key_for(k)] = rack_value_for(k, v) }
+        env.each_pair { |k, v| new_env[rack_key_for(k)] = rack_value_for(k, v) }
         new_env
       end
 
@@ -102,7 +102,9 @@ module ActionController
         method: ->(v) { v.upcase },
       }
 
-      def rack_key_for(key); RACK_KEY_TRANSLATION[key]; end
+      def rack_key_for(key)
+        RACK_KEY_TRANSLATION.fetch(key, key.to_s)
+      end
 
       def rack_value_for(key, value)
         RACK_VALUE_TRANSLATION.fetch(key, IDENTITY).call value