diff --git a/lib/capybara/server.rb b/lib/capybara/server.rb
index f59ddee0..dc04d615 100644
--- a/lib/capybara/server.rb
+++ b/lib/capybara/server.rb
@@ -33,10 +33,13 @@ module Capybara
 
     attr_reader :app, :port
 
-    def initialize(app)
+    def initialize(app, port=Capybara.server_port)
       @app = app
       @middleware = Middleware.new(@app)
       @server_thread = nil # supress warnings
+      @port = port
+      @port ||= Capybara::Server.ports[@app.object_id]
+      @port ||= find_available_port
     end
 
     def reset_error!
@@ -64,19 +67,14 @@ module Capybara
     end
 
     def boot
-      if @app
-        @port = Capybara::Server.ports[@app.object_id]
+      unless responsive?
+        Capybara::Server.ports[@app.object_id] = @port
 
-        if not @port or not responsive?
-          @port = Capybara.server_port || find_available_port
-          Capybara::Server.ports[@app.object_id] = @port
-
-          @server_thread = Thread.new do
-            Capybara.server.call(@middleware, @port)
-          end
-
-          Timeout.timeout(60) { @server_thread.join(0.1) until responsive? }
+        @server_thread = Thread.new do
+          Capybara.server.call(@middleware, @port)
         end
+
+        Timeout.timeout(60) { @server_thread.join(0.1) until responsive? }
       end
     rescue TimeoutError
       raise "Rack application timed out during boot"
diff --git a/lib/capybara/session.rb b/lib/capybara/session.rb
index f6b69c60..7e4571e6 100644
--- a/lib/capybara/session.rb
+++ b/lib/capybara/session.rb
@@ -50,8 +50,8 @@ module Capybara
     def initialize(mode, app=nil)
       @mode = mode
       @app = app
-      if Capybara.run_server and driver.needs_server?
-        @server = Capybara::Server.new(@app).tap(&:boot)
+      if Capybara.run_server and @app and driver.needs_server?
+        @server = Capybara::Server.new(@app).boot
       end
     end
 
diff --git a/spec/server_spec.rb b/spec/server_spec.rb
index 83f5d103..d4c83ae7 100644
--- a/spec/server_spec.rb
+++ b/spec/server_spec.rb
@@ -39,6 +39,16 @@ describe Capybara::Server do
     Capybara.server_port = nil
   end
 
+  it "should use given port" do
+    @app = proc { |env| [200, {}, "Hello Server!"]}
+    @server = Capybara::Server.new(@app, 22790).boot
+
+    @res = Net::HTTP.start(@server.host, 22790) { |http| http.get('/') }
+    @res.body.should include('Hello Server')
+
+    Capybara.server_port = nil
+  end
+
   it "should find an available port" do
     @app1 = proc { |env| [200, {}, "Hello Server!"]}
     @app2 = proc { |env| [200, {}, "Hello Second Server!"]}