diff --git a/stdlib/io-nonblock/0/io-nonblock.rbs b/stdlib/io-nonblock/0/io-nonblock.rbs
new file mode 100644
index 000000000..71a82fd7d
--- /dev/null
+++ b/stdlib/io-nonblock/0/io-nonblock.rbs
@@ -0,0 +1,68 @@
+%a{annotate:rdoc:skip}
+class IO
+  # <!--
+  #   rdoc-file=ext/io/nonblock/nonblock.c
+  #   - io.nonblock {|io| } -> object
+  #   - io.nonblock(boolean) {|io| } -> object
+  # -->
+  # Yields `self` in non-blocking mode.
+  #
+  # When `false` is given as an argument, `self` is yielded in blocking mode. The
+  # original mode is restored after the block is executed.
+  #
+  def nonblock: [T] (?boolish nb) { (self) -> T } -> T
+
+  # <!--
+  #   rdoc-file=ext/io/nonblock/nonblock.c
+  #   - io.nonblock = boolean -> boolean
+  # -->
+  # Enables non-blocking mode on a stream when set to `true`, and blocking mode
+  # when set to `false`.
+  #
+  # This method set or clear O_NONBLOCK flag for the file descriptor in *ios*.
+  #
+  # The behavior of most IO methods is not affected by this flag because they
+  # retry system calls to complete their task after EAGAIN and partial read/write.
+  # (An exception is IO#syswrite which doesn't retry.)
+  #
+  # This method can be used to clear non-blocking mode of standard I/O. Since
+  # nonblocking methods (read_nonblock, etc.) set non-blocking mode but they
+  # doesn't clear it, this method is usable as follows.
+  #
+  #     END { STDOUT.nonblock = false }
+  #     STDOUT.write_nonblock("foo")
+  #
+  # Since the flag is shared across processes and many non-Ruby commands doesn't
+  # expect standard I/O with non-blocking mode, it would be safe to clear the flag
+  # before Ruby program exits.
+  #
+  # For example following Ruby program leaves STDIN/STDOUT/STDER non-blocking
+  # mode. (STDIN, STDOUT and STDERR are connected to a terminal. So making one of
+  # them nonblocking-mode effects other two.) Thus cat command try to read from
+  # standard input and it causes "Resource temporarily unavailable" error
+  # (EAGAIN).
+  #
+  #     % ruby -e '
+  #     STDOUT.write_nonblock("foo\n")'; cat
+  #     foo
+  #     cat: -: Resource temporarily unavailable
+  #
+  # Clearing the flag makes the behavior of cat command normal. (cat command waits
+  # input from standard input.)
+  #
+  #     % ruby -rio/nonblock -e '
+  #     END { STDOUT.nonblock = false }
+  #     STDOUT.write_nonblock("foo")
+  #     '; cat
+  #     foo
+  #
+  def nonblock=: (boolish value) -> self
+
+  # <!--
+  #   rdoc-file=ext/io/nonblock/nonblock.c
+  #   - io.nonblock? -> boolean
+  # -->
+  # Returns `true` if an IO object is in non-blocking mode.
+  #
+  def nonblock?: () -> bool
+end
diff --git a/test/stdlib/IO_nonblock_test.rb b/test/stdlib/IO_nonblock_test.rb
new file mode 100644
index 000000000..12c61d1a0
--- /dev/null
+++ b/test/stdlib/IO_nonblock_test.rb
@@ -0,0 +1,37 @@
+require_relative "test_helper"
+require "io/nonblock"
+
+class IONonblockTest < Test::Unit::TestCase
+  include TestHelper
+
+  library "io-nonblock"
+  testing "::IO"
+
+  def setup
+    @r, @w = IO.pipe
+  end
+
+  def teardown
+    @r.close
+    @w.close
+  end
+
+  def test_nonblock
+    assert_send_type "() { (IO) -> Integer } -> Integer",
+                     @r, :nonblock do 1 end
+    assert_send_type "(bool) { (IO) -> Integer } -> Integer",
+                     @r, :nonblock, false do 1 end
+  end
+
+  def test_nonblock_assign
+    assert_send_type "(bool) -> IO",
+                     @r, :nonblock=, true
+    assert_send_type "(bool) -> IO",
+                     @r, :nonblock=, false
+  end
+
+  def test_nonblock?
+    assert_send_type "() -> bool",
+                     @r, :nonblock?
+  end
+end