diff --git a/sinatra.gemspec b/sinatra.gemspec
index 687284a5..fca444a4 100644
--- a/sinatra.gemspec
+++ b/sinatra.gemspec
@@ -104,7 +104,7 @@ 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', '>= 0.9.1', '< 1.0'
 
   s.has_rdoc = true
   s.homepage = "http://sinatra.rubyforge.org"