diff --git a/lib/sinatra/base.rb b/lib/sinatra/base.rb
index 582cae52..4a328ff3 100644
--- a/lib/sinatra/base.rb
+++ b/lib/sinatra/base.rb
@@ -43,7 +43,7 @@ module Sinatra
         body = [body] if body.respond_to? :to_str
         if body.respond_to?(:to_ary)
           header["Content-Length"] = body.to_ary.
-            inject(0) { |len, part| len + part.bytesize }.to_s
+            inject(0) { |len, part| len + Rack::Utils.bytesize(part) }.to_s
         end
         [status.to_i, header.to_hash, body]
       end
@@ -1106,13 +1106,3 @@ module Sinatra
     Default.helpers(*extensions, &block)
   end
 end
-
-class String #:nodoc:
-  # Define String#each under 1.9 for Rack compatibility. This should be
-  # removed once Rack is fully 1.9 compatible.
-  alias_method :each, :each_line  unless ''.respond_to? :each
-
-  # Define String#bytesize as an alias to String#length for Ruby 1.8.6 and
-  # earlier.
-  alias_method :bytesize, :length unless ''.respond_to? :bytesize
-end
diff --git a/sinatra.gemspec b/sinatra.gemspec
index ae50f1f7..10f8aae3 100644
--- a/sinatra.gemspec
+++ b/sinatra.gemspec
@@ -112,7 +112,7 @@ Gem::Specification.new do |s|
   s.test_files = s.files.select {|path| path =~ /^test\/.*_test.rb/}
 
   s.extra_rdoc_files = %w[README.rdoc LICENSE]
-  s.add_dependency 'rack',    '>= 0.9.1'
+  s.add_dependency 'rack',    '>= 1.0'
   s.add_development_dependency 'shotgun', '>= 0.2',   '< 1.0'
   s.add_development_dependency 'rack-test', '>= 0.3.0'