diff --git a/gri.gemspec b/gri.gemspec
index bb4215d..f761d42 100644
--- a/gri.gemspec
+++ b/gri.gemspec
@@ -15,5 +15,5 @@ Gem::Specification.new do |s|
   s.require_paths = ["lib"]
 
   s.add_development_dependency "msgpack"
-  s.add_runtime_dependency "rack"
+  s.add_runtime_dependency "rack", '< 3'
 end