diff --git a/lib/execjs/external_runtime.rb b/lib/execjs/external_runtime.rb
index f81bac6..65196cc 100644
--- a/lib/execjs/external_runtime.rb
+++ b/lib/execjs/external_runtime.rb
@@ -8,6 +8,7 @@ module ExecJS
       @runner_path = options[:runner_path]
       @test_args   = options[:test_args]
       @test_match  = options[:test_match]
+      @conversion  = options[:conversion]
       @binary      = locate_binary
     end
 
@@ -74,7 +75,7 @@ module ExecJS
       end
 
       def exec_runtime(filename)
-        output = `#{@binary} #{filename} 2>&1`
+        output = sh("#{@binary} #{filename} 2>&1")
         if $?.success?
           output
         else
@@ -82,6 +83,29 @@ module ExecJS
         end
       end
 
+      if "".respond_to?(:force_encoding)
+        def sh(command)
+          output, options = nil, {}
+          options[:internal_encoding] = @conversion[:from] if @conversion
+          IO.popen(command, options) { |f| output = f.read }
+          output.force_encoding(@conversion[:to]) if @conversion
+          output
+        end
+      else
+        require "iconv"
+
+        def sh(command)
+          output = nil
+          IO.popen(command) { |f| output = f.read }
+
+          if @conversion
+            Iconv.iconv(@conversion[:from], @conversion[:to], output).first
+          else
+            output
+          end
+        end
+      end
+
       def extract_result(output)
         status, value = output.empty? ? [] : JSON.parse(output)
         if status == "ok"
diff --git a/lib/execjs/runtimes.rb b/lib/execjs/runtimes.rb
index 018a3a4..cd20ec4 100644
--- a/lib/execjs/runtimes.rb
+++ b/lib/execjs/runtimes.rb
@@ -1,3 +1,4 @@
+
 module ExecJS
   module Runtimes
     def self.best_available
@@ -32,7 +33,8 @@ module ExecJS
 
     define_runtime :JavaScriptCore,
       :command => "/System/Library/Frameworks/JavaScriptCore.framework/Versions/A/Resources/jsc",
-      :runner_path => ExecJS.root + "/support/basic_runner.js"
+      :runner_path => ExecJS.root + "/support/basic_runner.js",
+      :conversion => { :from => "ISO8859-1", :to => "UTF-8" }
 
     define_runtime :Spidermonkey,
       :command => "js",