diff --git a/lib/mutant/mutator/node/resbody.rb b/lib/mutant/mutator/node/resbody.rb
index c91babfa..4560bd47 100644
--- a/lib/mutant/mutator/node/resbody.rb
+++ b/lib/mutant/mutator/node/resbody.rb
@@ -1,3 +1,5 @@
+# encoding: UTF-8
+
 module Mutant
   class Mutator
     class Node
diff --git a/spec/unit/mutant/subject/method/instance_spec.rb b/spec/unit/mutant/subject/method/instance_spec.rb
index 2eb1cae3..b9236024 100644
--- a/spec/unit/mutant/subject/method/instance_spec.rb
+++ b/spec/unit/mutant/subject/method/instance_spec.rb
@@ -1,3 +1,5 @@
+# encoding: UTF-8
+
 require 'spec_helper'
 
 describe Mutant::Subject::Method::Instance do