diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3e974948..094df87f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,15 +7,6 @@ jobs:
     strategy:
       matrix:
         include:
-          - gemfile: 5.2.gemfile
-            ruby: 2.5
-
-          - gemfile: 5.2.gemfile
-            ruby: 2.6
-
-          - gemfile: 5.2.gemfile
-            ruby: 2.7
-
           - gemfile: 6.0.gemfile
             ruby: 2.5
 
diff --git a/Gemfile b/Gemfile
index 8925d80d..c67483fc 100644
--- a/Gemfile
+++ b/Gemfile
@@ -6,3 +6,4 @@ gemspec
 
 gem "rubocop", require: false
 gem "codeclimate-test-reporter"
+gem "rack", "< 3"
diff --git a/gemfiles/5.2.gemfile b/gemfiles/5.2.gemfile
deleted file mode 100644
index 2530b2b9..00000000
--- a/gemfiles/5.2.gemfile
+++ /dev/null
@@ -1,7 +0,0 @@
-source "https://rubygems.org"
-
-gem "rubocop", require: false
-gem "codeclimate-test-reporter"
-gem "rails", "~> 5.2"
-
-gemspec path: "../"
diff --git a/gemfiles/6.0.gemfile b/gemfiles/6.0.gemfile
index 1283d3c9..4d97f903 100644
--- a/gemfiles/6.0.gemfile
+++ b/gemfiles/6.0.gemfile
@@ -3,5 +3,6 @@ source "https://rubygems.org"
 gem "rubocop", require: false
 gem "codeclimate-test-reporter"
 gem "rails", "~> 6.0"
+gem "concurrent-ruby", "< 1.3.5"
 
 gemspec path: "../"
diff --git a/gemfiles/6.1.gemfile b/gemfiles/6.1.gemfile
index 1d0b5256..b95e97e2 100644
--- a/gemfiles/6.1.gemfile
+++ b/gemfiles/6.1.gemfile
@@ -3,5 +3,6 @@ source "https://rubygems.org"
 gem "rubocop", require: false
 gem "codeclimate-test-reporter"
 gem "rails", "~> 6.1"
+gem "concurrent-ruby", "< 1.3.5"
 
 gemspec path: "../"
diff --git a/gemfiles/7.0.gemfile b/gemfiles/7.0.gemfile
index b659fbf1..1a33a37a 100644
--- a/gemfiles/7.0.gemfile
+++ b/gemfiles/7.0.gemfile
@@ -3,5 +3,7 @@ source "https://rubygems.org"
 gem "rubocop", require: false
 gem "codeclimate-test-reporter"
 gem "rails", "~> 7.0"
+gem "concurrent-ruby", "< 1.3.5"
+gem "rack", "< 3"
 
 gemspec path: "../"