diff --git a/lib/action_pack/cloudfront/ip_ranges.rb b/lib/action_pack/cloudfront/ip_ranges.rb
index d9bb1a7..d36413a 100644
--- a/lib/action_pack/cloudfront/ip_ranges.rb
+++ b/lib/action_pack/cloudfront/ip_ranges.rb
@@ -21,11 +21,11 @@ def ipaddr
       end
 
       def trusted_proxies
-        cloudfront_proxies + ActionDispatch::RemoteIp::TRUSTED_PROXIES
+        @trusted_proxies ||= (cloudfront_proxies + ActionDispatch::RemoteIp::TRUSTED_PROXIES).freeze
       end
 
       def cloudfront_proxies
-        ip_ranges.select(&:cloudfront?).map(&:ipaddr)
+        @cloudfront_proxies ||= (ip_ranges.select(&:cloudfront?).map(&:ipaddr)).freeze
       end
 
       def ip_ranges
@@ -35,7 +35,7 @@ def ip_ranges
           prefixesv6 = data['ipv6_prefixes']
           (prefixes + prefixesv6).map do |attrs|
             Range.new(attrs)
-          end
+          end.freeze
         end
       end
 
diff --git a/lib/action_pack/cloudfront/railtie.rb b/lib/action_pack/cloudfront/railtie.rb
index bba276b..87b13a6 100644
--- a/lib/action_pack/cloudfront/railtie.rb
+++ b/lib/action_pack/cloudfront/railtie.rb
@@ -12,7 +12,7 @@ class Railtie < ::Rails::Railtie
           trusted_proxies = ActionPack::Cloudfront::IpRanges.trusted_proxies
           existing_proxies = Array(app.config.action_dispatch.trusted_proxies)
 
-          app.config.action_dispatch.trusted_proxies = trusted_proxies.concat(existing_proxies).uniq
+          app.config.action_dispatch.trusted_proxies = (trusted_proxies + existing_proxies).uniq
         end
       end