diff --git a/lib/sprockets/encoding_utils.rb b/lib/sprockets/encoding_utils.rb
index d0bda9e02..32d63ea9c 100644
--- a/lib/sprockets/encoding_utils.rb
+++ b/lib/sprockets/encoding_utils.rb
@@ -1,5 +1,4 @@
 # frozen_string_literal: true
-require 'base64'
 require 'stringio'
 require 'zlib'
 
@@ -71,7 +70,7 @@ def gzip(str)
     #
     # Returns a encoded String
     def base64(str)
-      Base64.strict_encode64(str)
+      [str].pack("m0")
     end
 
 
diff --git a/test/fixtures/asset/sprite.css.erb b/test/fixtures/asset/sprite.css.erb
index e9f8c55bd..b276514ee 100644
--- a/test/fixtures/asset/sprite.css.erb
+++ b/test/fixtures/asset/sprite.css.erb
@@ -3,9 +3,8 @@
  */
 
 <%
-  require 'base64'
   path = File.expand_path("../POW.png", __FILE__)
-  data = Base64.encode64(File.open(path, "rb") { |f| f.read })
+  data = [File.open(path, "rb") { |f| f.read }].pack('m')
 %>
 .pow {
   background: url(data:image/png;base64,<%= data %>) no-repeat;
diff --git a/test/test_context.rb b/test/test_context.rb
index 1838242d4..164493152 100644
--- a/test/test_context.rb
+++ b/test/test_context.rb
@@ -47,8 +47,7 @@ def setup
   test "extend context" do
     @env.context_class.class_eval do
       def datauri(path)
-        require 'base64'
-        Base64.encode64(File.open(path, "rb") { |f| f.read })
+        [File.open(path, "rb") { |f| f.read }].pack('m')
       end
     end
 
@@ -89,14 +88,13 @@ def setup
     assert_equal "var Foo = {};\n\nvar Bar = {};\n", @env['application.js'].to_s
   end
 
-  require 'base64'
   DataUriProcessor = proc do |input|
     env = input[:environment]
     data = input[:data]
     data.gsub(/url\(\"(.+?)\"\)/) do
       uri, _ = env.resolve($1)
       path, _ = env.parse_asset_uri(uri)
-      data = Base64.encode64(File.open(path, "rb") { |f| f.read })
+      data = [File.open(path, "rb") { |f| f.read }].pack('m')
       "url(data:image/png;base64,#{data})"
     end
   end
@@ -111,14 +109,12 @@ def setup
   end
 
   test "block custom processor" do
-    require 'base64'
-
     @env.register_preprocessor 'text/css' do |input|
       env = input[:environment]
       input[:data].gsub(/url\(\"(.+?)\"\)/) do
         uri, _ = env.resolve($1)
         path, _ = env.parse_asset_uri(uri)
-        data = Base64.encode64(File.open(path, "rb") { |f| f.read })
+        data = [File.open(path, "rb") { |f| f.read }].pack('m')
         "url(data:image/png;base64,#{data})"
       end
     end