diff --git a/lib/execjs/duktape_runtime.rb b/lib/execjs/duktape_runtime.rb
index 7758fdf..60a1d38 100644
--- a/lib/execjs/duktape_runtime.rb
+++ b/lib/execjs/duktape_runtime.rb
@@ -6,21 +6,21 @@ module ExecJS
     class Context < Runtime::Context
       def initialize(runtime, source = "", options = {})
         @ctx = Duktape::Context.new(complex_object: nil)
-        @ctx.exec_string(encode(source), '(execjs)')
+        @ctx.exec_string(source.encode(Encoding::UTF_8), '(execjs)')
       rescue Exception => e
         raise wrap_error(e)
       end
 
       def exec(source, options = {})
         return unless /\S/ =~ source
-        @ctx.eval_string("(function(){#{encode(source)}})()", '(execjs)')
+        @ctx.eval_string("(function(){#{source.encode(Encoding::UTF_8)}})()", '(execjs)')
       rescue Exception => e
         raise wrap_error(e)
       end
 
       def eval(source, options = {})
         return unless /\S/ =~ source
-        @ctx.eval_string("(#{encode(source)})", '(execjs)')
+        @ctx.eval_string("(#{source.encode(Encoding::UTF_8)})", '(execjs)')
       rescue Exception => e
         raise wrap_error(e)
       end
diff --git a/lib/execjs/encoding.rb b/lib/execjs/encoding.rb
deleted file mode 100644
index 8296144..0000000
--- a/lib/execjs/encoding.rb
+++ /dev/null
@@ -1,26 +0,0 @@
-module ExecJS
-  # Encodes strings as UTF-8
-  module Encoding
-    if RUBY_ENGINE == 'jruby' || RUBY_ENGINE == 'rbx'
-      # workaround for jruby bug http://jira.codehaus.org/browse/JRUBY-6588
-      # workaround for rbx bug https://github.com/rubinius/rubinius/issues/1729
-      def encode(string)
-        if string.encoding == ::Encoding::BINARY
-          data = string.dup
-          data.force_encoding(::Encoding::UTF_8)
-
-          unless data.valid_encoding?
-            raise ::Encoding::UndefinedConversionError, "Could not encode binary data #{string.dump} as UTF-8"
-          end
-        else
-          data = string.encode(::Encoding::UTF_8)
-        end
-        data
-      end
-    else
-      def encode(string)
-        string.encode(::Encoding::UTF_8)
-      end
-    end
-  end
-end
diff --git a/lib/execjs/external_runtime.rb b/lib/execjs/external_runtime.rb
index 523bc5e..164587c 100644
--- a/lib/execjs/external_runtime.rb
+++ b/lib/execjs/external_runtime.rb
@@ -6,7 +6,7 @@ module ExecJS
   class ExternalRuntime < Runtime
     class Context < Runtime::Context
       def initialize(runtime, source = "", options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
 
         @runtime = runtime
         @source  = source
@@ -16,7 +16,7 @@ module ExecJS
       end
 
       def eval(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
 
         if /\S/ =~ source
           exec("return eval(#{::JSON.generate("(#{source})", quirks_mode: true)})")
@@ -24,7 +24,7 @@ module ExecJS
       end
 
       def exec(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
         source = "#{@source}\n#{source}" if @source != ""
         source = @runtime.compile_source(source)
 
diff --git a/lib/execjs/graaljs_runtime.rb b/lib/execjs/graaljs_runtime.rb
index d3cab2a..acb931a 100644
--- a/lib/execjs/graaljs_runtime.rb
+++ b/lib/execjs/graaljs_runtime.rb
@@ -8,7 +8,7 @@ module ExecJS
         @context.eval('js', 'delete this.console')
         @js_object = @context.eval('js', 'Object')
 
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
         unless source.empty?
           translate do
             eval_in_context(source)
@@ -17,7 +17,7 @@ module ExecJS
       end
 
       def exec(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
         source = "(function(){#{source}})()" if /\S/.match?(source)
 
         translate do
@@ -26,7 +26,7 @@ module ExecJS
       end
 
       def eval(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
         source = "(#{source})" if /\S/.match?(source)
 
         translate do
@@ -35,7 +35,7 @@ module ExecJS
       end
 
       def call(source, *args)
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
         source = "(#{source})" if /\S/.match?(source)
 
         translate do
diff --git a/lib/execjs/mini_racer_runtime.rb b/lib/execjs/mini_racer_runtime.rb
index 9b66bbf..47c005c 100644
--- a/lib/execjs/mini_racer_runtime.rb
+++ b/lib/execjs/mini_racer_runtime.rb
@@ -4,7 +4,7 @@ module ExecJS
   class MiniRacerRuntime < Runtime
     class Context < Runtime::Context
       def initialize(runtime, source = "", options={})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
         @context = ::MiniRacer::Context.new
         @context.eval("delete this.console");
         translate do
@@ -13,7 +13,7 @@ module ExecJS
       end
 
       def exec(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
 
         if /\S/ =~ source
           eval "(function(){#{source}})()"
@@ -21,7 +21,7 @@ module ExecJS
       end
 
       def eval(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
 
         if /\S/ =~ source
           translate do
diff --git a/lib/execjs/ruby_rhino_runtime.rb b/lib/execjs/ruby_rhino_runtime.rb
index b740b72..4829263 100644
--- a/lib/execjs/ruby_rhino_runtime.rb
+++ b/lib/execjs/ruby_rhino_runtime.rb
@@ -5,7 +5,7 @@ module ExecJS
   class RubyRhinoRuntime < Runtime
     class Context < Runtime::Context
       def initialize(runtime, source = "", options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
 
         @rhino_context = ::Rhino::Context.new
         fix_memory_limit! @rhino_context
@@ -15,7 +15,7 @@ module ExecJS
       end
 
       def exec(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
 
         if /\S/ =~ source
           eval "(function(){#{source}})()", options
@@ -23,7 +23,7 @@ module ExecJS
       end
 
       def eval(source, options = {})
-        source = encode(source)
+        source = source.encode(Encoding::UTF_8)
 
         if /\S/ =~ source
           unbox @rhino_context.eval("(#{source})")
diff --git a/lib/execjs/runtime.rb b/lib/execjs/runtime.rb
index 822bf5a..726e57b 100644
--- a/lib/execjs/runtime.rb
+++ b/lib/execjs/runtime.rb
@@ -1,11 +1,7 @@
-require "execjs/encoding"
-
 module ExecJS
   # Abstract base class for runtimes
   class Runtime
     class Context
-      include Encoding
-
       def initialize(runtime, source = "", options = {})
       end