diff --git a/gemfiles/Gemfile.beta-versions b/gemfiles/Gemfile.beta-versions
index 09ff70fa..3aed1438 100644
--- a/gemfiles/Gemfile.beta-versions
+++ b/gemfiles/Gemfile.beta-versions
@@ -14,3 +14,5 @@ gem 'rspec-mocks', github: 'rspec/rspec-mocks'
 gem 'rspec-expectations', github: 'rspec/rspec-expectations'
 gem 'cucumber', github: 'cucumber/cucumber-ruby'
 
+gem 'puma', github: 'puma/puma'
+
diff --git a/gemfiles/Gemfile.edge-marionette b/gemfiles/Gemfile.edge-marionette
index d5a7e0b8..301beec5 100644
--- a/gemfiles/Gemfile.edge-marionette
+++ b/gemfiles/Gemfile.edge-marionette
@@ -8,3 +8,5 @@ gem 'xpath', github: 'teamcapybara/xpath'
 gem 'selenium-webdriver', :path => '../../selenium/build/rb'
 gem 'rack', github: 'rack/rack'
 gem 'sinatra', github: 'sinatra/sinatra', branch: 'master'
+
+gem 'puma', github: 'puma/puma'
\ No newline at end of file
diff --git a/gemfiles/Gemfile.rspec-34 b/gemfiles/Gemfile.rspec-34
index 6cb23f38..d4886d82 100644
--- a/gemfiles/Gemfile.rspec-34
+++ b/gemfiles/Gemfile.rspec-34
@@ -5,4 +5,3 @@ gemspec :path => '..'
 
 gem 'xpath', github: 'teamcapybara/xpath'
 gem 'rspec', '~>3.4.0'
-
diff --git a/lib/capybara.rb b/lib/capybara.rb
index 97e5d691..51e517d3 100644
--- a/lib/capybara.rb
+++ b/lib/capybara.rb
@@ -232,7 +232,7 @@ module Capybara
     # @param [Integer] port              The port to run the application on
     #
     def run_default_server(app, port)
-      servers[:webrick].call(app, port, server_host)
+      servers[:puma].call(app, port, server_host)
     end
 
     ##
diff --git a/lib/capybara/spec/test_app.rb b/lib/capybara/spec/test_app.rb
index 4e197b71..34396746 100644
--- a/lib/capybara/spec/test_app.rb
+++ b/lib/capybara/spec/test_app.rb
@@ -186,5 +186,5 @@ class TestApp < Sinatra::Base
 end
 
 if __FILE__ == $0
-  Rack::Handler::WEBrick.run TestApp, Port: 8070
+  Rack::Handler::Puma.run TestApp, Port: 8070
 end
diff --git a/spec/capybara_spec.rb b/spec/capybara_spec.rb
index 17adfa77..d36f9e4f 100644
--- a/spec/capybara_spec.rb
+++ b/spec/capybara_spec.rb
@@ -79,6 +79,19 @@ RSpec.describe Capybara do
     end
   end
 
+  describe "server=" do
+    after do
+      Capybara.server = :default
+    end
+
+    it "should have a :webrick server registered" do
+      Capybara.server = :webrick
+      session = Capybara::Session.new(:selenium, TestApp.new)
+      session.visit('/')
+      expect(session.body).to include("Hello world!")
+    end
+  end
+
   describe 'app_host' do
     after do
       Capybara.app_host = nil
diff --git a/spec/server_spec.rb b/spec/server_spec.rb
index ee9acfc1..aef4fd68 100644
--- a/spec/server_spec.rb
+++ b/spec/server_spec.rb
@@ -98,24 +98,23 @@ RSpec.describe Capybara::Server do
     end
 
     it "detects and waits for all reused server sessions pending requests" do
-      done = false
+      done = 0
 
       app = proc do |env|
         request = Rack::Request.new(env)
         sleep request.params['wait_time'].to_f
-        done = true
+        done += 1
         [200, {}, ["Hello Server!"]]
       end
 
       server1 = Capybara::Server.new(app).boot
       server2 = Capybara::Server.new(app).boot
 
-      start_request(server1, 0.5)
-      start_request(server2, 1.0)
-
       expect {
+        start_request(server1, 1.0)
+        start_request(server2, 3.0)
         server1.wait_for_pending_requests
-      }.to change{done}.from(false).to(true)
+      }.to change{done}.from(0).to(2)
       expect(server2.send(:pending_requests?)).to eq(false)
     end
 
@@ -147,25 +146,27 @@ RSpec.describe Capybara::Server do
     end
 
     it "detects and waits for only one sessions pending requests" do
-      done = false
+      done = 0
 
       app = proc do |env|
         request = Rack::Request.new(env)
         sleep request.params['wait_time'].to_f
-        done = true
+        done += 1
         [200, {}, ["Hello Server!"]]
       end
 
       server1 = Capybara::Server.new(app).boot
       server2 = Capybara::Server.new(app).boot
 
-      start_request(server1, 0.5)
-      start_request(server2, 1.0)
-
       expect {
+        start_request(server1, 1.0)
+        start_request(server2, 3.0)
         server1.wait_for_pending_requests
-      }.to change{done}.from(false).to(true)
+      }.to change{done}.from(0).to(1)
       expect(server2.send(:pending_requests?)).to eq(true)
+      expect {
+        server2.wait_for_pending_requests
+      }.to change{done}.from(1).to(2)
     end
 
   end
@@ -199,6 +200,7 @@ RSpec.describe Capybara::Server do
     # Start request, but don't wait for it to finish
     socket = TCPSocket.new(server.host, server.port)
     socket.write "GET /?wait_time=#{wait_time.to_s} HTTP/1.0\r\n\r\n"
+    sleep 0.1
     socket.close
     sleep 0.1
   end