diff --git a/test/io/nonblock/test_flush.rb b/test/io/nonblock/test_flush.rb
new file mode 100644
index 0000000000..5ca4beba60
--- /dev/null
+++ b/test/io/nonblock/test_flush.rb
@@ -0,0 +1,22 @@
+require 'test/unit'
+require 'io/nonblock'
+
+class TestIONonblock < Test::Unit::TestCase
+  def test_flush                # [ruby-dev:24985]
+    r,w = IO.pipe
+    w.nonblock = true
+    w.sync = false
+    w << "b"
+    w.flush
+    w << "a" * 4096
+    Thread.new {
+      Thread.pass
+      w.close
+    }
+    Thread.new {
+      Thread.pass
+      nil while r.read(4096)
+    }
+    assert_raise(IOError) {w.flush}
+  end
+end