diff --git a/test/psych/test_emitter.rb b/test/psych/test_emitter.rb
index c90765349a..3738c1ac04 100644
--- a/test/psych/test_emitter.rb
+++ b/test/psych/test_emitter.rb
@@ -6,7 +6,7 @@ module Psych
   class TestEmitter < TestCase
     def setup
       super
-      @out = StringIO.new
+      @out = StringIO.new('')
       @emitter = Psych::Emitter.new @out
     end