diff --git a/mailcatcher.gemspec b/mailcatcher.gemspec
index b7e1cbc8e..f83d105d5 100644
--- a/mailcatcher.gemspec
+++ b/mailcatcher.gemspec
@@ -36,10 +36,10 @@ Gem::Specification.new do |s|
   s.add_dependency "faye-websocket", "~> 0.11.1"
   s.add_dependency "mail", "~> 2.3"
   s.add_dependency "net-smtp"
-  s.add_dependency "rack", "~> 2.2"
-  s.add_dependency "sinatra", "~> 3.2"
+  s.add_dependency "rack", "~> 3.2"
+  s.add_dependency "sinatra", "~> 4.2"
   s.add_dependency "sqlite3", "~> 1.3"
-  s.add_dependency "thin", "~> 1.8"
+  s.add_dependency "thin", "~> 2.0"
 
   s.add_development_dependency "capybara"
   s.add_development_dependency "capybara-screenshot"