diff --git a/ChangeLog b/ChangeLog
index 3ca07fbbee..4251ee485c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Apr 27 15:47:54 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/stringio/stringio.c (strio_s_new): warn if a block is given,
+	  as well as IO.new.
+
 Wed Apr 27 14:29:47 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* error.c (ruby_only_for_internal_use): raise fatal error when
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index bd83ea207b..368dcfec4b 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -241,6 +241,19 @@ strio_s_open(int argc, VALUE *argv, VALUE klass)
     return rb_ensure(rb_yield, obj, strio_finalize, obj);
 }
 
+/* :nodoc: */
+static VALUE
+strio_s_new(int argc, VALUE *argv, VALUE klass)
+{
+    if (rb_block_given_p()) {
+	VALUE cname = rb_obj_as_string(klass);
+
+	rb_warn("%"PRIsVALUE"::new() does not take block; use %"PRIsVALUE"::open() instead",
+		cname, cname);
+    }
+    return rb_class_new_instance(argc, argv, klass);
+}
+
 /*
  * Returns +false+.  Just for compatibility to IO.
  */
@@ -1523,6 +1536,7 @@ Init_stringio(void)
 
     rb_include_module(StringIO, rb_mEnumerable);
     rb_define_alloc_func(StringIO, strio_s_allocate);
+    rb_define_singleton_method(StringIO, "new", strio_s_new, -1);
     rb_define_singleton_method(StringIO, "open", strio_s_open, -1);
     rb_define_method(StringIO, "initialize", strio_initialize, -1);
     rb_define_method(StringIO, "initialize_copy", strio_copy, 1);
diff --git a/test/stringio/test_stringio.rb b/test/stringio/test_stringio.rb
index e443fa6c26..bf3a9eeb1b 100644
--- a/test/stringio/test_stringio.rb
+++ b/test/stringio/test_stringio.rb
@@ -674,4 +674,10 @@ class TestStringIO < Test::Unit::TestCase
     bug_11945 = '[ruby-core:72699] [Bug #11945]'
     assert_equal Encoding::ASCII_8BIT, s.external_encoding, bug_11945
   end
+
+  def test_new_block_warning
+    assert_warn(/does not take block/) do
+      StringIO.new {}
+    end
+  end
 end