diff --git a/ruby/lib/plus_codes.rb b/ruby/lib/plus_codes.rb
index c64a8ef8..0efdc428 100644
--- a/ruby/lib/plus_codes.rb
+++ b/ruby/lib/plus_codes.rb
@@ -1,15 +1,17 @@
+# frozen_string_literal: true
+
 # Plus+Codes is a Ruby implementation of Google Open Location Code (Plus Codes).
 #
 # @author We-Ming Wu
 module PlusCodes
   # The character set used to encode coordinates.
-  CODE_ALPHABET = '23456789CFGHJMPQRVWX'.freeze
+  CODE_ALPHABET = '23456789CFGHJMPQRVWX'
 
   # The character used to pad a code
-  PADDING = '0'.freeze
+  PADDING = '0'
 
   # A separator used to separate the code into two parts.
-  SEPARATOR = '+'.freeze
+  SEPARATOR = '+'
 
   # The max number of characters can be placed before the separator.
   SEPARATOR_POSITION = 8
diff --git a/ruby/lib/plus_codes/code_area.rb b/ruby/lib/plus_codes/code_area.rb
index acae335c..b3fb9d07 100644
--- a/ruby/lib/plus_codes/code_area.rb
+++ b/ruby/lib/plus_codes/code_area.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module PlusCodes
   # [CodeArea] contains coordinates of a decoded Open Location Code(Plus+Codes).
   # The coordinates include the latitude and longitude of the lower left and
diff --git a/ruby/lib/plus_codes/open_location_code.rb b/ruby/lib/plus_codes/open_location_code.rb
index 6ebe7fe9..7c6e4628 100644
--- a/ruby/lib/plus_codes/open_location_code.rb
+++ b/ruby/lib/plus_codes/open_location_code.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require_relative '../plus_codes'
 require_relative '../plus_codes/code_area'
 
diff --git a/ruby/open-location-code.gemspec b/ruby/open-location-code.gemspec
index 8853cb1f..b95e5afa 100644
--- a/ruby/open-location-code.gemspec
+++ b/ruby/open-location-code.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 'date'
diff --git a/ruby/test/plus_codes_test.rb b/ruby/test/plus_codes_test.rb
index ce615102..38d86640 100644
--- a/ruby/test/plus_codes_test.rb
+++ b/ruby/test/plus_codes_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require 'test/unit'
 require_relative '../lib/plus_codes/open_location_code'