diff --git a/mailcatcher.gemspec b/mailcatcher.gemspec
index a943e05..25b2aea 100644
--- a/mailcatcher.gemspec
+++ b/mailcatcher.gemspec
@@ -30,7 +30,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '>= 1.8.7'
 
-  s.add_dependency "activesupport", ">= 3.0.0", "< 4.1"
+  s.add_dependency "activesupport", ">= 3.0.0", "< 5"
   s.add_dependency "eventmachine", "~> 1.0.0"
   s.add_dependency "haml", ">= 3.1", "< 4.1"
   s.add_dependency "mail", "~> 2.3"