diff --git a/sinatra.gemspec b/sinatra.gemspec
index 9548a6bc..34918c2a 100644
--- a/sinatra.gemspec
+++ b/sinatra.gemspec
@@ -12,7 +12,7 @@ Gem::Specification.new 'sinatra', Sinatra::VERSION do |s|
   s.extra_rdoc_files  = s.files.select { |p| p =~ /^README/ } << 'LICENSE'
   s.rdoc_options      = %w[--line-numbers --inline-source --title Sinatra --main README.rdoc]
 
-  s.add_dependency 'rack',            '~> 1.3'
-  s.add_dependency 'rack-protection', '~> 1.1'
-  s.add_dependency 'tilt',            '~> 1.3'
+  s.add_dependency 'rack',            '~> 1.3', '>= 1.3.4'
+  s.add_dependency 'rack-protection', '~> 1.1', '>= 1.1.2'
+  s.add_dependency 'tilt',            '~> 1.3', '>= 1.3.3'
 end