diff --git a/cztop.gemspec b/cztop.gemspec
index 98f0839..06287e3 100644
--- a/cztop.gemspec
+++ b/cztop.gemspec
@@ -32,4 +32,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "pry"
   spec.add_development_dependency "yard"
   spec.add_development_dependency "rubocop", "~> 1.36.0"
+  spec.add_development_dependency "async", ">= 2.0.1"
+  spec.add_development_dependency "async-io"
 end
diff --git a/lib/cztop/async.rb b/lib/cztop/async.rb
index c3c133a..1138a00 100644
--- a/lib/cztop/async.rb
+++ b/lib/cztop/async.rb
@@ -5,6 +5,18 @@
 
 module Async
   module IO
+
+    # Wrapper for CZTop sockets.
+    #
+    # @example
+    #   Async do |task|
+    #     socket = CZTop::Socket::REP.new("ipc:///tmp/req_rep_example")
+    #     socket.options.rcvtimeo = 3
+    #     io = Async::IO.try_convert socket
+    #     msg = io.receive
+    #     io << msg.to_a.map(&:upcase)
+    #   end
+
     class CZTopSocket < Generic
       wraps ::CZTop::Socket::REQ
       wraps ::CZTop::Socket::REP
@@ -19,20 +31,22 @@ class CZTopSocket < Generic
       wraps ::CZTop::Socket::XSUB
 
 
+      # @see {CZTop::SendReceiveMethods#receive}
       def receive
         wait_readable
         @io.receive
       end
 
 
+      # @see {CZTop::SendReceiveMethods#<<}
       def <<(...)
         wait_writable
         @io.<<(...)
       end
 
 
+      # Waits for socket to become readable.
       def wait_readable(timeout = read_timeout)
-        puts "Async::IO::CZTopSocket#wait_readable: waiting with timeout=#{timeout}"
         @io_fd ||= ::IO.for_fd @io.fd, autoclose: false
 
         if timeout
@@ -41,7 +55,7 @@ def wait_readable(timeout = read_timeout)
           while true
             @io_fd.wait_readable(timeout)
             break if @io.readable?
-            raise TimeoutError if now >= timeout_at
+            raise ::IO::TimeoutError if now >= timeout_at
           end
         else
           @io_fd.wait_readable until @io.readable?
@@ -49,8 +63,8 @@ def wait_readable(timeout = read_timeout)
       end
 
 
+      # Waits for socket to become writable.
       def wait_writable(timeout = write_timeout)
-        puts "Async::IO::CZTopSocket#wait_writable: waiting with timeout=#{timeout}"
         @io_fd ||= ::IO.for_fd @io.fd, autoclose: false
 
         if timeout
@@ -59,7 +73,7 @@ def wait_writable(timeout = write_timeout)
           while true
             @io_fd.wait_writable(timeout)
             break if @io.writable?
-            raise TimeoutError if now >= timeout_at
+            raise ::IO::TimeoutError if now >= timeout_at
           end
         else
           @io_fd.wait_writable until @io.writable?
@@ -67,16 +81,30 @@ def wait_writable(timeout = write_timeout)
       end
 
 
+      # @return [Float, nil] the timeout in seconds used by {IO#wait_readable}
       def read_timeout
         timeout = @io.options.rcvtimeo
-        timeout = nil if timeout <= 0
+
+        if timeout <= 0
+          timeout = nil
+        else
+          timeout = timeout.to_f / 1000
+        end
+
         timeout
       end
 
 
+      # @return [Float, nil] the timeout in seconds used by {IO#wait_writable}
       def write_timeout
         timeout = @io.options.sndtimeo
-        timeout = nil if timeout <= 0
+
+        if timeout <= 0
+          timeout = nil
+        else
+          timeout = timeout.to_f / 1000
+        end
+
         timeout
       end
 
diff --git a/lib/cztop/zsock_options.rb b/lib/cztop/zsock_options.rb
index 16f005c..c5fcf6b 100644
--- a/lib/cztop/zsock_options.rb
+++ b/lib/cztop/zsock_options.rb
@@ -264,29 +264,33 @@ def PLAIN_password=(password)
 
       # @!group Send and Receive Timeouts
 
-      # @return [Integer] the timeout when receiving a message
+      # @return [Integer] the timeout in milliseconds when receiving a message
       # @see Message.receive_from
+      # @note -1 means infinite, 0 means nonblocking
       def rcvtimeo
         Zsock.rcvtimeo(@zocket)
       end
 
 
-      # @param timeout [Integer] new timeout
+      # @param timeout [Integer] new timeout in milliseconds
       # @see Message.receive_from
+      # @note -1 means infinite, 0 means nonblocking
       def rcvtimeo=(timeout)
         Zsock.set_rcvtimeo(@zocket, timeout)
       end
 
 
-      # @return [Integer] the timeout when sending a message
+      # @return [Integer] the timeout in milliseconds when sending a message
       # @see Message#send_to
+      # @note -1 means infinite, 0 means nonblocking
       def sndtimeo
         Zsock.sndtimeo(@zocket)
       end
 
 
-      # @param timeout [Integer] new timeout
+      # @param timeout [Integer] new timeout in milliseconds
       # @see Message#send_to
+      # @note -1 means infinite, 0 means nonblocking
       def sndtimeo=(timeout)
         Zsock.set_sndtimeo(@zocket, timeout)
       end
diff --git a/spec/cztop/async_spec.rb b/spec/cztop/async_spec.rb
new file mode 100644
index 0000000..fb315a5
--- /dev/null
+++ b/spec/cztop/async_spec.rb
@@ -0,0 +1,160 @@
+# frozen_string_literal: true
+
+require_relative 'spec_helper'
+require_relative '../../lib/cztop/async'
+
+describe Async::IO::CZTopSocket do
+  i = 0
+  let(:endpoint)   { "inproc://async_endpoint_socket_spec_reqrep_#{i += 1}" }
+  let(:req_socket) { CZTop::Socket::REQ.new(endpoint) }
+  let(:rep_socket) { CZTop::Socket::REP.new(endpoint) }
+  let(:req_io)     { Async::IO.try_convert req_socket }
+  let(:rep_io)     { Async::IO.try_convert rep_socket }
+
+
+  it 'can be converted to Async::IO' do
+    assert_kind_of Async::IO::CZTopSocket, req_io
+    assert_kind_of Async::IO::CZTopSocket, rep_io
+  end
+
+  it 'can send and receive' do
+    Async do |task|
+      rep_socket
+      req_socket
+
+      sleep 0.1
+      req_io = Async::IO.try_convert req_socket
+      rep_io = Async::IO.try_convert rep_socket
+
+      task.async do |task|
+        msg = rep_io.receive
+        word, = msg.to_a
+        rep_io << word.upcase
+      end
+
+      task.async do |task|
+        req_io << 'hello'
+        response, = req_io.receive.to_a
+        # p response: response
+        assert_equal 'HELLO', response
+      end
+    end
+  end
+
+
+  describe '#read_timeout' do
+    describe 'with no rcvtimeout set' do
+      before do
+        assert_equal -1, req_socket.options.rcvtimeo
+      end
+
+      it 'returns nil' do
+        assert_nil req_io.read_timeout
+      end
+    end
+
+    # NOTE: 0 would mean non-block (EAGAIN), but that's obsolete with Async
+    describe 'with no rcvtimeout=0' do
+      before do
+        req_socket.options.rcvtimeo = 0
+      end
+
+      it 'returns nil' do
+        assert_nil req_io.read_timeout
+      end
+    end
+
+    describe 'with rcvtimeout set' do
+      before do
+        req_socket.options.rcvtimeo = 10 # ms
+      end
+
+      it 'returns timeout in seconds' do
+        assert_equal 0.01, req_io.read_timeout
+      end
+    end
+  end
+
+
+  describe '#write_timeout' do
+    describe 'with no sndtimeout set' do
+      before do
+        assert_equal -1, req_socket.options.sndtimeo
+      end
+
+      it 'returns nil' do
+        assert_nil req_io.write_timeout
+      end
+    end
+
+    # NOTE: 0 would mean non-block (EAGAIN), but that's obsolete with Async
+    describe 'with sndtimeout=0' do
+      before do
+        req_socket.options.sndtimeo = 0
+      end
+
+      it 'returns nil' do
+        assert_nil req_io.write_timeout
+      end
+    end
+
+    describe 'with sndtimeout set' do
+      before do
+        req_socket.options.sndtimeo = 10
+      end
+
+      it 'returns timeout in seconds' do
+        assert_equal 0.01, req_io.write_timeout
+      end
+    end
+  end
+
+
+  context 'with rcvtimeo' do
+    before do
+      req_socket.options.rcvtimeo = 30
+      assert_equal 30, req_socket.options.rcvtimeo
+    end
+
+    it 'will raise TimeoutError' do
+      Async do
+        assert_raises ::IO::TimeoutError do
+          req_io.receive
+        end
+      end
+    end
+  end
+
+
+  context 'with sndtimeo' do
+    before do
+      rep_socket.options.sndtimeo = 30
+      assert_equal 30, rep_socket.options.sndtimeo
+    end
+
+    it 'will raise TimeoutError' do
+      Async do
+        assert_raises ::IO::TimeoutError do
+          rep_io << ['foo']
+        end
+      end
+    end
+  end
+
+
+  describe 'thread-safe sockets', if: has_czmq_drafts? do
+    let(:endpoint)      { "inproc://async_endpoint_socket_spec_serverclient_#{i += 1}" }
+    let(:server_socket) { CZTop::Socket::SERVER.new(endpoint) }
+    let(:client_socket) { CZTop::Socket::CLIENT.new(endpoint) }
+
+    it 'does not convert thread-safe sockets' do
+      assert_raises ArgumentError do
+        Async::IO.try_convert server_socket
+      end
+
+      assert_raises ArgumentError do
+        Async::IO.try_convert client_socket
+      end
+    end
+  end
+end
diff --git a/spec/cztop/zsock_options_spec.rb b/spec/cztop/zsock_options_spec.rb
index 2ae5eee..9971b5a 100644
--- a/spec/cztop/zsock_options_spec.rb
+++ b/spec/cztop/zsock_options_spec.rb
@@ -245,8 +245,12 @@
     describe '#sndtimeo' do
       it 'sets and gets send timeout' do
         assert_equal(-1, options.sndtimeo)
+
         options.sndtimeo = 7
         assert_equal 7, options.sndtimeo
+
+        options.sndtimeo = 0
+        assert_equal 0, options.sndtimeo
       end
     end