diff --git a/test/ruby/test_regexp.rb b/test/ruby/test_regexp.rb
index 3324a9e8d9..c9488dc713 100644
--- a/test/ruby/test_regexp.rb
+++ b/test/ruby/test_regexp.rb
@@ -819,9 +819,9 @@ class TestRegexp < Test::Unit::TestCase
   end
 
   def test_dup_warn
-    assert_in_out_err('-w', 'x=/[\u3042\u3041]/', [], /\A\z/)
-    assert_in_out_err('-w', 'x=/[\u3042\u3042]/', [], /duplicated/)
-    assert_in_out_err('-w', 'x=/[\u3042\u3041-\u3043]/', [], /duplicated/)
+    assert_in_out_err('-w', 'x=/[\\u3042\\u3041]/', [], /\A\z/)
+    assert_in_out_err('-w', 'x=/[\\u3042\\u3042]/', [], /duplicated/)
+    assert_in_out_err('-w', 'x=/[\\u3042\\u3041-\\u3043]/', [], /duplicated/)
   end
 
   def test_property_warn