diff --git a/Gemfile b/Gemfile
index a537bd3da3f..f3d30946a77 100644
--- a/Gemfile
+++ b/Gemfile
@@ -57,7 +57,7 @@ gem 'rqrcode'
 gem 'ruby-progressbar'
 gem 'ruby-saml'
 gem 'safe_target_blank', '>= 1.0.2'
-gem 'saml_idp', github: '18F/saml_idp', tag: '0.18.0-18f'
+gem 'saml_idp', github: '18F/saml_idp', tag: '0.18.1-18f'
 gem 'scrypt'
 gem 'simple_form', '>= 5.0.2'
 gem 'sprockets-rails'
diff --git a/Gemfile.lock b/Gemfile.lock
index f451b897bfe..b64ab9b8a32 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -25,8 +25,8 @@ GIT
 
 GIT
   remote: https://github.com/18F/saml_idp.git
-  revision: 7f516c9e2c608ac92ee0c41daecfdb9208c7ec5a
-  tag: 0.18.0-18f
+  revision: d8e7deb7da3aa43bae0e5b0891c8de123d492484
+  tag: 0.18.1-18f
   specs:
     saml_idp (0.18.0.pre.18f)
       activesupport
@@ -34,7 +34,6 @@ GIT
       faraday
       nokogiri (>= 1.10.2)
       pkcs11
-      uuid
 
 GIT
   remote: https://github.com/hashrocket/capybara-webmock.git
@@ -380,8 +379,6 @@ GEM
       zeitwerk (~> 2.5)
     lru_redux (1.1.0)
     lumberjack (1.2.8)
-    macaddr (1.7.2)
-      systemu (~> 2.6.5)
     mail (2.7.1)
       mini_mime (>= 0.1.1)
     marcel (1.0.2)
@@ -645,7 +642,6 @@ GEM
       activerecord (>= 5.2)
     strscan (3.0.5)
     subprocess (1.5.5)
-    systemu (2.6.5)
     terminal-table (3.0.2)
       unicode-display_width (>= 1.1.1, < 3)
     thor (1.2.1)
@@ -663,8 +659,6 @@ GEM
     unf_ext (0.0.8)
     unicode-display_width (2.4.0)
     uniform_notifier (1.16.0)
-    uuid (2.3.9)
-      macaddr (~> 1.0)
     valid_email (0.1.4)
       activemodel
       mail (>= 2.6.1)
diff --git a/app/controllers/saml_idp_controller.rb b/app/controllers/saml_idp_controller.rb
index c7650735abb..665d8e40934 100644
--- a/app/controllers/saml_idp_controller.rb
+++ b/app/controllers/saml_idp_controller.rb
@@ -1,6 +1,5 @@
 require 'saml_idp_constants'
 require 'saml_idp'
-require 'uuid'
 
 class SamlIdpController < ApplicationController
   include SamlIdp::Controller
diff --git a/config/initializers/ahoy.rb b/config/initializers/ahoy.rb
index ebbcfb5ffb9..e24e13fdee3 100644
--- a/config/initializers/ahoy.rb
+++ b/config/initializers/ahoy.rb
@@ -60,14 +60,8 @@ def event_logger
     end
 
     def invalid_uuid?(token)
-      # The match? method does not exist for the Regexp class in Ruby < 2.4
-      # Here, it comes from Active Support. Once we upgrade to Ruby 2.5,
-      # we probably want to ignore the Rails definition and use Ruby's.
-      # To do that, we'll need to set `config.active_support.bare = true`,
-      # and then only require the extensions we use.
       token = Utf8Cleaner.new(token).remove_invalid_utf8_bytes
-      uuid_regex = /\A[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\z/
-      !uuid_regex.match?(token)
+      !Idp::Constants::UUID_REGEX.match?(token)
     end
   end
 end
diff --git a/lib/idp/constants.rb b/lib/idp/constants.rb
index f3b8f77c5dd..760795e4831 100644
--- a/lib/idp/constants.rb
+++ b/lib/idp/constants.rb
@@ -1,5 +1,6 @@
 module Idp
   module Constants
+    UUID_REGEX = /\A[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\z/
     module Vendors
       ACUANT = 'acuant'
       LEXIS_NEXIS = 'lexis_nexis'
diff --git a/spec/controllers/saml_idp_controller_spec.rb b/spec/controllers/saml_idp_controller_spec.rb
index 57dd0fbcf3c..526e49ff524 100644
--- a/spec/controllers/saml_idp_controller_spec.rb
+++ b/spec/controllers/saml_idp_controller_spec.rb
@@ -1582,7 +1582,7 @@ def name_id_version(format_urn)
         end
 
         it 'includes an ID attribute with a valid UUID' do
-          expect(UUID.validate(assertion['ID'][1..-1])).to eq(true)
+          expect(Idp::Constants::UUID_REGEX.match?(assertion['ID'][1..-1])).to eq(true)
           expect(assertion['ID']).to eq "_#{user.last_identity.session_uuid}"
         end
 
@@ -1705,7 +1705,7 @@ def name_id_version(format_urn)
           end
 
           it 'includes a URI attribute' do
-            expect(UUID.validate(reference['URI'][2..-1])).to eq(true)
+            expect(Idp::Constants::UUID_REGEX.match?(reference['URI'][2..-1])).to eq(true)
           end
         end
       end