diff --git a/mandrill-rails.gemspec b/mandrill-rails.gemspec
index 78b127a..df054e1 100644
--- a/mandrill-rails.gemspec
+++ b/mandrill-rails.gemspec
@@ -16,7 +16,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.version       = Mandrill::Rails::VERSION
 
-  spec.add_runtime_dependency "activesupport", ">= 5"
+  spec.add_runtime_dependency "activesupport", ">= 4"
 
   spec.add_development_dependency "bundler", "~> 1.14"
   spec.add_development_dependency "rake", "~> 10.0"