diff --git a/lib/sidekiq/web/action.rb b/lib/sidekiq/web/action.rb
index 5b9c0a83..5adc91e5 100644
--- a/lib/sidekiq/web/action.rb
+++ b/lib/sidekiq/web/action.rb
@@ -2,9 +2,9 @@
 
 module Sidekiq
   class WebAction
-    RACK_SESSION = 'rack.session'
-    TEXT_HTML = { "Content-Type" => "text/html", "Cache-Control" => "no-cache" }
-    APPLICATION_JSON = { "Content-Type" => "application/json", "Cache-Control" => "no-cache" }
+    RACK_SESSION = 'rack.session'.freeze
+    TEXT_HTML = { "Content-Type" => "text/html", "Cache-Control" => "no-cache" }.freeze
+    APPLICATION_JSON = { "Content-Type" => "application/json", "Cache-Control" => "no-cache" }.freeze
 
     attr_accessor :env, :block, :type
 
diff --git a/lib/sidekiq/web/application.rb b/lib/sidekiq/web/application.rb
index fc26f69a..c16b5fef 100644
--- a/lib/sidekiq/web/application.rb
+++ b/lib/sidekiq/web/application.rb
@@ -7,7 +7,7 @@ module Sidekiq
     CONTENT_LENGTH = "Content-Length".freeze
     CONTENT_TYPE = "Content-Type".freeze
     REDIS_KEYS = %w(redis_version uptime_in_days connected_clients used_memory_human used_memory_peak_human)
-    NOT_FOUND = [404, {"Content-Type" => "text/plain", "X-Cascade" => "pass" }, ["Not Found"]]
+    NOT_FOUND = [404, {"Content-Type" => "text/plain", "X-Cascade" => "pass" }.freeze, ["Not Found"]]
 
     def initialize(klass)
       @klass = klass
@@ -290,6 +290,8 @@ module Sidekiq
         [200, type_header, [resp]]
       end
 
+      resp[1] = resp[1].dup
+
       resp[1][CONTENT_LENGTH] = resp[2].inject(0) { |l, p| l + p.bytesize }.to_s
 
       resp