diff --git a/Gemfile b/Gemfile
index 32e1a575..05fc138f 100644
--- a/Gemfile
+++ b/Gemfile
@@ -32,6 +32,8 @@ gem "phonelib"
 ###############
 
 gem "audited", "~> 5.4"
+gem "concurrent-ruby", require: "concurrent"
+gem "concurrent-ruby-ext"
 gem "config", "~> 4.2"
 gem "devise", "~> 4.9"
 gem "flipper"
diff --git a/Gemfile.lock b/Gemfile.lock
index 7ad12716..c8c09b58 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -100,6 +100,8 @@ GEM
       xpath (~> 3.2)
     coderay (1.1.3)
     concurrent-ruby (1.2.2)
+    concurrent-ruby-ext (1.2.2)
+      concurrent-ruby (= 1.2.2)
     config (4.2.1)
       deep_merge (~> 1.2, >= 1.2.1)
       dry-validation (~> 1.0, >= 1.0.0)
@@ -476,6 +478,8 @@ DEPENDENCIES
   brakeman
   bundler-audit
   capybara
+  concurrent-ruby
+  concurrent-ruby-ext
   config (~> 4.2)
   dartsass-rails (~> 0.5.0)
   debug
diff --git a/app/models/urn.rb b/app/models/urn.rb
index 2160c548..9a2a31ad 100644
--- a/app/models/urn.rb
+++ b/app/models/urn.rb
@@ -77,7 +77,7 @@ def next(route)
   private
 
     def routes
-      @routes ||= Hash.new do |hash, route|
+      @routes ||= Concurrent::Hash.new do |hash, route|
         hash[route] = urn_enumerator(
           config.codes.fetch(route),
           config.seeds.fetch(route, Random.new_seed),
@@ -102,7 +102,7 @@ def available_urns(code, seed, used_urns)
     end
 
     def urn_enumerator(code, seed, used_urns)
-      list = available_urns(code, seed, used_urns)
+      list = Concurrent::Array.new(available_urns(code, seed, used_urns))
       error_msg = "you have exhausted urn for code #{code} you need to increase the size of the suffix"
 
       Enumerator.new do |yielder|