diff --git a/Gemfile b/Gemfile
index 1b55f12..0b883d8 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 source 'https://rubygems.org'
 gemspec name: 'classifier-reborn'
diff --git a/Rakefile b/Rakefile
index c2169a2..7e6b9f4 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'rubygems'
 require 'rake'
 require 'rake/testtask'
diff --git a/classifier-reborn-jruby.gemspec b/classifier-reborn-jruby.gemspec
index d06388e..5e69a42 100644
--- a/classifier-reborn-jruby.gemspec
+++ b/classifier-reborn-jruby.gemspec
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 lib = File.expand_path('lib', __dir__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'classifier-reborn/version'
@@ -7,7 +9,7 @@ Gem::Specification.new do |s|
   s.specification_version = 2 if s.respond_to? :specification_version=
   s.required_rubygems_version = Gem::Requirement.new('>= 0') if s.respond_to? :required_rubygems_version=
   s.rubygems_version = '2.2.2'
-  s.required_ruby_version = '>= 2.2'
+  s.required_ruby_version = '>= 2.4.0'
 
   s.name             = 'classifier-reborn-jruby'
   s.version          = ClassifierReborn::VERSION
diff --git a/classifier-reborn.gemspec b/classifier-reborn.gemspec
index f6289a3..1db93fd 100644
--- a/classifier-reborn.gemspec
+++ b/classifier-reborn.gemspec
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 lib = File.expand_path('lib', __dir__)
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'classifier-reborn/version'
@@ -6,7 +8,7 @@ Gem::Specification.new do |s|
   s.specification_version = 2 if s.respond_to? :specification_version=
   s.required_rubygems_version = Gem::Requirement.new('>= 0') if s.respond_to? :required_rubygems_version=
   s.rubygems_version = '2.2.2'
-  s.required_ruby_version = '>= 2.2'
+  s.required_ruby_version = '>= 2.4.0'
 
   s.name             = 'classifier-reborn'
   s.version          = ClassifierReborn::VERSION
diff --git a/lib/classifier-reborn.rb b/lib/classifier-reborn.rb
index 4461792..eac3737 100644
--- a/lib/classifier-reborn.rb
+++ b/lib/classifier-reborn.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 #--
 # Copyright (c) 2005 Lucas Carlson
 #
diff --git a/lib/classifier-reborn/backends/bayes_memory_backend.rb b/lib/classifier-reborn/backends/bayes_memory_backend.rb
index 2ea370a..5d359ae 100644
--- a/lib/classifier-reborn/backends/bayes_memory_backend.rb
+++ b/lib/classifier-reborn/backends/bayes_memory_backend.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ClassifierReborn
   class BayesMemoryBackend
     attr_reader :total_words, :total_trainings
diff --git a/lib/classifier-reborn/backends/bayes_redis_backend.rb b/lib/classifier-reborn/backends/bayes_redis_backend.rb
index 758c3f7..db95772 100644
--- a/lib/classifier-reborn/backends/bayes_redis_backend.rb
+++ b/lib/classifier-reborn/backends/bayes_redis_backend.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative 'no_redis_error'
 # require redis when we run #intialize. This way only people using this backend
 # will need to install and load the backend without having to
diff --git a/lib/classifier-reborn/backends/no_redis_error.rb b/lib/classifier-reborn/backends/no_redis_error.rb
index eb4a97d..9a9c323 100644
--- a/lib/classifier-reborn/backends/no_redis_error.rb
+++ b/lib/classifier-reborn/backends/no_redis_error.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class NoRedisError < RuntimeError
   def initialize
     msg =
diff --git a/lib/classifier-reborn/bayes.rb b/lib/classifier-reborn/bayes.rb
index 97c9b26..10a43eb 100644
--- a/lib/classifier-reborn/bayes.rb
+++ b/lib/classifier-reborn/bayes.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/category_namer.rb b/lib/classifier-reborn/category_namer.rb
index 559aaa4..e204bd0 100644
--- a/lib/classifier-reborn/category_namer.rb
+++ b/lib/classifier-reborn/category_namer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/extensions/hasher.rb b/lib/classifier-reborn/extensions/hasher.rb
index efef4b2..ff482ce 100644
--- a/lib/classifier-reborn/extensions/hasher.rb
+++ b/lib/classifier-reborn/extensions/hasher.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/extensions/token_filter/stemmer.rb b/lib/classifier-reborn/extensions/token_filter/stemmer.rb
index 41eeebe..4949d64 100644
--- a/lib/classifier-reborn/extensions/token_filter/stemmer.rb
+++ b/lib/classifier-reborn/extensions/token_filter/stemmer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/extensions/token_filter/stopword.rb b/lib/classifier-reborn/extensions/token_filter/stopword.rb
index d514225..9276b79 100644
--- a/lib/classifier-reborn/extensions/token_filter/stopword.rb
+++ b/lib/classifier-reborn/extensions/token_filter/stopword.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/extensions/token_filter/symbol.rb b/lib/classifier-reborn/extensions/token_filter/symbol.rb
index 9fade99..1cc4db0 100644
--- a/lib/classifier-reborn/extensions/token_filter/symbol.rb
+++ b/lib/classifier-reborn/extensions/token_filter/symbol.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/extensions/tokenizer/token.rb b/lib/classifier-reborn/extensions/tokenizer/token.rb
index 1b2b465..547cbbf 100644
--- a/lib/classifier-reborn/extensions/tokenizer/token.rb
+++ b/lib/classifier-reborn/extensions/tokenizer/token.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/extensions/tokenizer/whitespace.rb b/lib/classifier-reborn/extensions/tokenizer/whitespace.rb
index ee1ffe3..ba6a528 100644
--- a/lib/classifier-reborn/extensions/tokenizer/whitespace.rb
+++ b/lib/classifier-reborn/extensions/tokenizer/whitespace.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/extensions/vector.rb b/lib/classifier-reborn/extensions/vector.rb
index ef23589..1b0594d 100644
--- a/lib/classifier-reborn/extensions/vector.rb
+++ b/lib/classifier-reborn/extensions/vector.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Ernest Ellingson
 # Copyright:: Copyright (c) 2005
 
diff --git a/lib/classifier-reborn/extensions/vector_serialize.rb b/lib/classifier-reborn/extensions/vector_serialize.rb
index 988f680..a25c506 100644
--- a/lib/classifier-reborn/extensions/vector_serialize.rb
+++ b/lib/classifier-reborn/extensions/vector_serialize.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module GSL
   class Vector
     def _dump(_v)
diff --git a/lib/classifier-reborn/extensions/zero_vector.rb b/lib/classifier-reborn/extensions/zero_vector.rb
index c08f78a..57bfaa3 100644
--- a/lib/classifier-reborn/extensions/zero_vector.rb
+++ b/lib/classifier-reborn/extensions/zero_vector.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Vector
   def zero?
     all?(&:zero?)
diff --git a/lib/classifier-reborn/lsi.rb b/lib/classifier-reborn/lsi.rb
index 4b00a4a..378f1da 100644
--- a/lib/classifier-reborn/lsi.rb
+++ b/lib/classifier-reborn/lsi.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    David Fayram  (mailto:dfayram@lensmen.net)
 # Copyright:: Copyright (c) 2005 David Fayram II
 # License::   LGPL
diff --git a/lib/classifier-reborn/lsi/cached_content_node.rb b/lib/classifier-reborn/lsi/cached_content_node.rb
index 4c2b28b..88c2dd4 100644
--- a/lib/classifier-reborn/lsi/cached_content_node.rb
+++ b/lib/classifier-reborn/lsi/cached_content_node.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Kelley Reynolds  (mailto:kelley@insidesystems.net)
 # Copyright:: Copyright (c) 2015 Kelley Reynolds
 # License::   LGPL
diff --git a/lib/classifier-reborn/lsi/content_node.rb b/lib/classifier-reborn/lsi/content_node.rb
index 920664a..91872b8 100644
--- a/lib/classifier-reborn/lsi/content_node.rb
+++ b/lib/classifier-reborn/lsi/content_node.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    David Fayram  (mailto:dfayram@lensmen.net)
 # Copyright:: Copyright (c) 2005 David Fayram II
 # License::   LGPL
diff --git a/lib/classifier-reborn/lsi/summarizer.rb b/lib/classifier-reborn/lsi/summarizer.rb
index 89e9b4c..31dc97d 100644
--- a/lib/classifier-reborn/lsi/summarizer.rb
+++ b/lib/classifier-reborn/lsi/summarizer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    Lucas Carlson  (mailto:lucas@rufy.com)
 # Copyright:: Copyright (c) 2005 Lucas Carlson
 # License::   LGPL
diff --git a/lib/classifier-reborn/lsi/word_list.rb b/lib/classifier-reborn/lsi/word_list.rb
index 74547f4..0f929f8 100644
--- a/lib/classifier-reborn/lsi/word_list.rb
+++ b/lib/classifier-reborn/lsi/word_list.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Author::    David Fayram  (mailto:dfayram@lensmen.net)
 # Copyright:: Copyright (c) 2005 David Fayram II
 # License::   LGPL
diff --git a/lib/classifier-reborn/validators/classifier_validator.rb b/lib/classifier-reborn/validators/classifier_validator.rb
index 41d6d17..90edb93 100644
--- a/lib/classifier-reborn/validators/classifier_validator.rb
+++ b/lib/classifier-reborn/validators/classifier_validator.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ClassifierReborn
   module ClassifierValidator
     module_function
diff --git a/lib/classifier-reborn/version.rb b/lib/classifier-reborn/version.rb
index 9b553d8..cc89b67 100644
--- a/lib/classifier-reborn/version.rb
+++ b/lib/classifier-reborn/version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ClassifierReborn
-  VERSION = '2.2.0'.freeze
+  VERSION = '2.2.0'
 end
diff --git a/test/backends/backend_common_tests.rb b/test/backends/backend_common_tests.rb
index d29d15d..c755184 100644
--- a/test/backends/backend_common_tests.rb
+++ b/test/backends/backend_common_tests.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module BackendCommonTests
   def test_initial_values
     assert @backend.total_words.zero?
diff --git a/test/backends/backend_memory_test.rb b/test/backends/backend_memory_test.rb
index d132790..ef6c058 100644
--- a/test/backends/backend_memory_test.rb
+++ b/test/backends/backend_memory_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require_relative './backend_common_tests'
 
diff --git a/test/backends/backend_redis_test.rb b/test/backends/backend_redis_test.rb
index f55f663..b33ba0e 100644
--- a/test/backends/backend_redis_test.rb
+++ b/test/backends/backend_redis_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require_relative './backend_common_tests'
 
diff --git a/test/bayes/bayesian_common_benchmarks.rb b/test/bayes/bayesian_common_benchmarks.rb
index cdae4aa..f6f8685 100644
--- a/test/bayes/bayesian_common_benchmarks.rb
+++ b/test/bayes/bayesian_common_benchmarks.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module BayesianCommonBenchmarks
   MAX_RECORDS = 5000
 
diff --git a/test/bayes/bayesian_common_tests.rb b/test/bayes/bayesian_common_tests.rb
index b6fcbac..43eda15 100644
--- a/test/bayes/bayesian_common_tests.rb
+++ b/test/bayes/bayesian_common_tests.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module BayesianCommonTests
   def test_good_training
     assert_equal ['love'], @classifier.train_interesting('love')
diff --git a/test/bayes/bayesian_integration_test.rb b/test/bayes/bayesian_integration_test.rb
index 8cfca91..3b5d1a2 100644
--- a/test/bayes/bayesian_integration_test.rb
+++ b/test/bayes/bayesian_integration_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require_relative '../data/test_data_loader'
 
diff --git a/test/bayes/bayesian_memory_benchmark.rb b/test/bayes/bayesian_memory_benchmark.rb
index 2e70904..7fc1a42 100755
--- a/test/bayes/bayesian_memory_benchmark.rb
+++ b/test/bayes/bayesian_memory_benchmark.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require_relative './bayesian_common_benchmarks'
 require_relative '../data/test_data_loader'
diff --git a/test/bayes/bayesian_memory_test.rb b/test/bayes/bayesian_memory_test.rb
index b8c25df..8247009 100755
--- a/test/bayes/bayesian_memory_test.rb
+++ b/test/bayes/bayesian_memory_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require_relative './bayesian_common_tests'
 
diff --git a/test/bayes/bayesian_redis_benchmark.rb b/test/bayes/bayesian_redis_benchmark.rb
index 3ee0f41..5a0a1d4 100644
--- a/test/bayes/bayesian_redis_benchmark.rb
+++ b/test/bayes/bayesian_redis_benchmark.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require_relative './bayesian_common_benchmarks'
 require_relative '../data/test_data_loader'
diff --git a/test/bayes/bayesian_redis_test.rb b/test/bayes/bayesian_redis_test.rb
index 41bfeb4..0cb51ac 100644
--- a/test/bayes/bayesian_redis_test.rb
+++ b/test/bayes/bayesian_redis_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require_relative './bayesian_common_tests'
 
diff --git a/test/data/test_data_loader.rb b/test/data/test_data_loader.rb
index 67c88f7..4f4d12e 100644
--- a/test/data/test_data_loader.rb
+++ b/test/data/test_data_loader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module TestDataLoader
   def self.sms_data
     @@sms_data ||= load_sms_data
diff --git a/test/extensions/hasher_test.rb b/test/extensions/hasher_test.rb
index cecd285..0b5a49a 100644
--- a/test/extensions/hasher_test.rb
+++ b/test/extensions/hasher_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../test_helper'
 require 'tempfile'
 
diff --git a/test/extensions/matrix_test.rb b/test/extensions/matrix_test.rb
index acfa8b0..385fb8f 100644
--- a/test/extensions/matrix_test.rb
+++ b/test/extensions/matrix_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class MatrixTest < Minitest::Test
   def test_zero_division
     matrix = Matrix[[1, 0], [0, 1]]
diff --git a/test/extensions/token_filter/stemmer_test.rb b/test/extensions/token_filter/stemmer_test.rb
index fb493fa..7da31be 100644
--- a/test/extensions/token_filter/stemmer_test.rb
+++ b/test/extensions/token_filter/stemmer_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 require 'tempfile'
 
diff --git a/test/extensions/token_filter/stopword_test.rb b/test/extensions/token_filter/stopword_test.rb
index c39ccf5..3f7a932 100644
--- a/test/extensions/token_filter/stopword_test.rb
+++ b/test/extensions/token_filter/stopword_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 require 'tempfile'
 
diff --git a/test/extensions/token_filter/symbol_test.rb b/test/extensions/token_filter/symbol_test.rb
index 5d27fa7..f317897 100644
--- a/test/extensions/token_filter/symbol_test.rb
+++ b/test/extensions/token_filter/symbol_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 require 'tempfile'
 
diff --git a/test/extensions/tokenizer/token_test.rb b/test/extensions/tokenizer/token_test.rb
index 4db2693..0ec00b8 100644
--- a/test/extensions/tokenizer/token_test.rb
+++ b/test/extensions/tokenizer/token_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 require 'tempfile'
 
diff --git a/test/extensions/tokenizer/whitespace_test.rb b/test/extensions/tokenizer/whitespace_test.rb
index b7da528..f724cc3 100644
--- a/test/extensions/tokenizer/whitespace_test.rb
+++ b/test/extensions/tokenizer/whitespace_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../../test_helper'
 require 'tempfile'
 
diff --git a/test/extensions/zero_vector_test.rb b/test/extensions/zero_vector_test.rb
index 2c9c9fa..dff079f 100644
--- a/test/extensions/zero_vector_test.rb
+++ b/test/extensions/zero_vector_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ZeroVectorTest < Minitest::Test
   def test_zero?
     vec0 = Vector[]
diff --git a/test/lsi/lsi_test.rb b/test/lsi/lsi_test.rb
index 75ff819..0efe3c1 100644
--- a/test/lsi/lsi_test.rb
+++ b/test/lsi/lsi_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 
 class LSITest < Minitest::Test
diff --git a/test/lsi/word_list_test.rb b/test/lsi/word_list_test.rb
index 3b9153a..9655a97 100644
--- a/test/lsi/word_list_test.rb
+++ b/test/lsi/word_list_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../test_helper'
 
 class WordListTest < Minitest::Test
diff --git a/test/test_helper.rb b/test/test_helper.rb
index a56f265..632ba44 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 $LOAD_PATH.unshift(File.dirname(__FILE__) + '/../lib')
 
 require 'minitest/autorun'
diff --git a/test/validators/classifier_validation.rb b/test/validators/classifier_validation.rb
index 36246b2..c336426 100644
--- a/test/validators/classifier_validation.rb
+++ b/test/validators/classifier_validation.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require File.dirname(__FILE__) + '/../test_helper'
 require File.dirname(__FILE__) + '/../../lib/classifier-reborn/validators/classifier_validator'
 require_relative '../data/test_data_loader'