diff --git a/lib/rack/builder.rb b/lib/rack/builder.rb
index e708b52ae..2a643beb3 100644
--- a/lib/rack/builder.rb
+++ b/lib/rack/builder.rb
@@ -22,6 +22,10 @@ def initialize(&block)
       instance_eval(&block) if block_given?
     end
 
+    def self.app(&block)
+      self.new(&block).to_app
+    end
+
     def use(middleware, *args, &block)
       @ins << if block_given?
         lambda { |app| middleware.new(app, *args, &block) }
diff --git a/test/spec_rack_builder.rb b/test/spec_rack_builder.rb
index 2a0b46500..fbf32e045 100644
--- a/test/spec_rack_builder.rb
+++ b/test/spec_rack_builder.rb
@@ -47,4 +47,15 @@
     response.body.to_s.should.equal 'Hi Boss'
   end
 
+  specify "has explicit #to_app" do
+    app = Rack::Builder.app do
+      use Rack::ShowExceptions
+      run lambda { |env| raise "bzzzt" }
+    end
+
+    Rack::MockRequest.new(app).get("/").should.be.server_error
+    Rack::MockRequest.new(app).get("/").should.be.server_error
+    Rack::MockRequest.new(app).get("/").should.be.server_error
+  end
+
 end