diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index e2c4641..6e0a5d3 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -12,7 +12,6 @@ jobs:
       matrix:
         gemfile: [Gemfile]
         ruby:
-          - "2.3"
           - "2.4"
           - "2.5"
           - "2.6"
diff --git a/lib/uglifier.rb b/lib/uglifier.rb
index e705ab6..473b9ab 100644
--- a/lib/uglifier.rb
+++ b/lib/uglifier.rb
@@ -1,7 +1,6 @@
 # encoding: UTF-8
 
 require "json"
-require "base64"
 require "execjs"
 require "uglifier/version"
 
@@ -160,7 +159,7 @@ def initialize(options = {})
   def compile(source)
     if @options[:source_map]
       compiled, source_map = run_uglifyjs(source, true)
-      source_map_uri = Base64.strict_encode64(source_map)
+      source_map_uri = [source_map].pack('m0')
       source_map_mime = "application/json;charset=utf-8;base64"
       compiled + "\n//# sourceMappingURL=data:#{source_map_mime},#{source_map_uri}"
     else
@@ -512,7 +511,7 @@ def input_source_map(source, generate_map)
     source_map_options = @options[:source_map].is_a?(Hash) ? @options[:source_map] : {}
     sanitize_map_root(source_map_options.fetch(:input_source_map) do
       url = extract_source_mapping_url(source)
-      Base64.strict_decode64(url.split(",", 2)[-1]) if url && url.start_with?("data:")
+      url.split(",", 2)[-1].unpack1('m0') if url && url.start_with?("data:")
     end)
   rescue ArgumentError, JSON::ParserError
     nil
diff --git a/uglifier.gemspec b/uglifier.gemspec
index 6e555a4..d88e2fe 100644
--- a/uglifier.gemspec
+++ b/uglifier.gemspec
@@ -13,7 +13,7 @@ Gem::Specification.new do |spec|
   spec.description = "Uglifier minifies JavaScript files by wrapping UglifyJS to be accessible in Ruby"
   spec.license = "MIT"
 
-  spec.required_ruby_version = '>= 1.9.3'
+  spec.required_ruby_version = '>= 2.4.0'
 
   spec.extra_rdoc_files = [
     "LICENSE.txt",