diff --git a/Gemfile.lock b/Gemfile.lock
index 064d59c..50d398f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -12,7 +12,7 @@ PATH
   specs:
     mcp_server (0.1.0)
       mcp (~> 0.1)
-      rack (~> 2.0)
+      rack (>= 2, < 4)
 
 GEM
   remote: https://rubygems.org/
@@ -36,7 +36,7 @@ GEM
     prism (1.4.0)
     public_suffix (6.0.2)
     racc (1.8.1)
-    rack (2.2.17)
+    rack (2.2.19)
     rainbow (3.1.1)
     rake (13.3.0)
     regexp_parser (2.10.0)
diff --git a/mcp_server.gemspec b/mcp_server.gemspec
index 709da9f..0b43179 100644
--- a/mcp_server.gemspec
+++ b/mcp_server.gemspec
@@ -9,7 +9,7 @@ Gem::Specification.new do |spec|
   spec.homepage = "http://your-gem-homepage"
   spec.license = "MIT"
 
-  spec.add_dependency "rack", "~> 2.0"
+  spec.add_dependency "rack", ">= 2", "< 4"
   spec.add_dependency "mcp", "~> 0.1"
 
   spec.add_development_dependency "minitest", "~> 5.0"