diff --git a/ChangeLog b/ChangeLog
index cc5a90e83e..f712c238dd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Oct  8 16:36:47 2014    <>
+
+	* test/ruby/test_syntax.rb: added syntax tests of underscore arguments.
+	  [Feature #10340][ruby-core:65496]
+
 Wed Oct  8 07:42:39 2014  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* lib/uri/generic.rb (URI#inspect): remove Object id.
diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index 475ee99a33..564a7eab29 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -204,18 +204,22 @@ WARN
 
   def test_duplicated_arg
     assert_syntax_error("def foo(a, a) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_, _) end }
   end
 
   def test_duplicated_rest
     assert_syntax_error("def foo(a, *a) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_, *_) end }
   end
 
   def test_duplicated_opt
     assert_syntax_error("def foo(a, a=1) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_, _=1) end }
   end
 
   def test_duplicated_opt_rest
     assert_syntax_error("def foo(a=1, *a) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_=1, *_) end }
   end
 
   def test_duplicated_rest_opt
@@ -228,30 +232,37 @@ WARN
 
   def test_duplicated_opt_post
     assert_syntax_error("def foo(a=1, a) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_=1, _) end }
   end
 
   def test_duplicated_kw
     assert_syntax_error("def foo(a, a: 1) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_, _: 1) end }
   end
 
   def test_duplicated_rest_kw
     assert_syntax_error("def foo(*a, a: 1) end", /duplicated argument name/)
+    assert_nothing_raised {def foo(*_, _: 1) end}
   end
 
   def test_duplicated_opt_kw
     assert_syntax_error("def foo(a=1, a: 1) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_=1, _: 1) end }
   end
 
   def test_duplicated_kw_kwrest
     assert_syntax_error("def foo(a: 1, **a) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_: 1, **_) end }
   end
 
   def test_duplicated_rest_kwrest
     assert_syntax_error("def foo(*a, **a) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(*_, **_) end }
   end
 
   def test_duplicated_opt_kwrest
     assert_syntax_error("def foo(a=1, **a) end", /duplicated argument name/)
+    assert_nothing_raised { def foo(_=1, **_) end }
   end
 
   def test_duplicated_when