gistfile1.txt

diff --git a/lib/sinatra/base.rb b/lib/sinatra/base.rb
index 1d0cbe6..46d9d7b 100644
--- a/lib/sinatra/base.rb
+++ b/lib/sinatra/base.rb
@@ -49,7 +49,7 @@ module Sinatra
       else
         body = @body || []
         body = [body] if body.respond_to? :to_str
-        if header["Content-Length"].nil? && body.respond_to?(:to_ary)
+        if body.respond_to?(:to_ary)
           header["Content-Length"] = body.to_ary.
             inject(0) { |len, part| len + part.bytesize }.to_s
         end
diff --git a/test/base_test.rb b/test/base_test.rb
index cdddb5f..fae3bc7 100644
--- a/test/base_test.rb
+++ b/test/base_test.rb
@@ -109,4 +109,21 @@ describe "Sinatra::Base as Rack middleware" do
     assert_equal 'true', response['X-Downstream']
     assert_equal 'Hello after explicit forward', response.body
   end
+
+  app_content_length = lambda {|env|
+    [200, {'Content-Length' => '16'}, 'From downstream!']}
+  class TestMiddlewareContentLength < Sinatra::Base
+    get '/forward' do
+      res = forward
+      'From after explicit forward!'
+    end
+  end
+
+  middleware_content_length = TestMiddlewareContentLength.new(app_content_length)
+  request_content_length = Rack::MockRequest.new(middleware_content_length)
+
+  it "sets content length from last upstream body" do
+    response = request_content_length.get('/forward')
+    assert_equal '28', response['Content-Length']
+  end
 end