diff --git a/.gitignore b/.gitignore
index 7fde878..a864bfb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 .bundle
 .config
 .ruby-version
+.tool-versions
 .yardoc
 .idea/
 enumerize.iml
diff --git a/.tool-versions b/.tool-versions
deleted file mode 100644
index 59511e1..0000000
--- a/.tool-versions
+++ /dev/null
@@ -1 +0,0 @@
-ruby 2.7.8
diff --git a/Gemfile.global b/Gemfile.global
index 0a1e177..7dab5d7 100644
--- a/Gemfile.global
+++ b/Gemfile.global
@@ -8,7 +8,7 @@ if ENV['TEST_FRAMEWORK'] == 'rspec'
   gem 'rspec', :require => false
 end
 
-gem 'pg', '~> 1.5.3', :platform => [:ruby, :mswin, :mingw]
+gem 'pg', '~> 1.5.3', platforms: [:ruby, :mswin, :mingw]
 gem 'sequel'
 gem 'simple_form'
 gem 'formtastic'
diff --git a/Gemfile.mongo_mapper b/Gemfile.mongo_mapper
index 2eb7ae9..27e8bb4 100644
--- a/Gemfile.mongo_mapper
+++ b/Gemfile.mongo_mapper
@@ -3,4 +3,7 @@ eval_gemfile('Gemfile.global')
 gem 'minitest', '~> 5.8'
 gem 'rails',    github: 'rails/rails', branch: '7-0-stable', require: false
 gem 'mongo_mapper'
-gem 'sqlite3', :platform => [:ruby, :mswin, :mingw]
+
+# This Rails version has a pessimistic version constraint on sqlite3:
+# https://github.com/rails/rails/blob/7-0-stable/Gemfile#L148
+gem 'sqlite3', '~> 1.6', '>= 1.6.6', platforms: [:ruby, :mswin, :mingw]
diff --git a/Gemfile.rails61 b/Gemfile.rails61
index 3910089..fe0c705 100644
--- a/Gemfile.rails61
+++ b/Gemfile.rails61
@@ -3,4 +3,7 @@ eval_gemfile('Gemfile.global')
 gem 'minitest', '~> 5.8'
 gem 'rails',    github: 'rails/rails', branch: '6-1-stable', require: false
 gem 'mongoid',  github: 'mongodb/mongoid'
-gem 'sqlite3', :platform => [:ruby, :mswin, :mingw]
+
+# This Rails version has a pessimistic version constraint on sqlite3:
+# https://github.com/rails/rails/blob/6-1-stable/Gemfile#L143
+gem 'sqlite3', '~> 1.4', platforms: [:ruby, :mswin, :mingw]
diff --git a/Gemfile.rails70 b/Gemfile.rails70
index 53e9bed..93f6029 100644
--- a/Gemfile.rails70
+++ b/Gemfile.rails70
@@ -5,4 +5,6 @@ gem 'rails',    github: 'rails/rails', branch: '7-0-stable', require: false
 
 gem 'mongoid',  github: 'mongodb/mongoid'
 
-gem 'sqlite3', :platform => [:ruby, :mswin, :mingw]
+# This Rails version has a pessimistic version constraint on sqlite3:
+# https://github.com/rails/rails/blob/7-0-stable/Gemfile#L148
+gem 'sqlite3', '~> 1.6', '>= 1.6.6', platforms: [:ruby, :mswin, :mingw]
diff --git a/Gemfile.rails71 b/Gemfile.rails71
index 2691f0b..448f83d 100644
--- a/Gemfile.rails71
+++ b/Gemfile.rails71
@@ -5,4 +5,4 @@ gem 'rails',    github: 'rails/rails', branch: '7-1-stable', require: false
 
 gem 'mongoid',  github: 'mongodb/mongoid'
 
-gem 'sqlite3', :platform => [:ruby, :mswin, :mingw]
+gem 'sqlite3', platforms: [:ruby, :mswin, :mingw]
diff --git a/Gemfile.railsmaster b/Gemfile.railsmaster
index 53145f5..1ddfe99 100644
--- a/Gemfile.railsmaster
+++ b/Gemfile.railsmaster
@@ -2,4 +2,4 @@ eval_gemfile('Gemfile.global')
 
 gem 'minitest', '~> 5.8'
 gem 'rails',    github: 'rails/rails', branch: 'main', require: false
-gem 'sqlite3', :platform => [:ruby, :mswin, :mingw]
+gem 'sqlite3', platforms: [:ruby, :mswin, :mingw]