diff --git a/time_difference.gemspec b/time_difference.gemspec
index 5ece9c4..f8833d3 100644
--- a/time_difference.gemspec
+++ b/time_difference.gemspec
@@ -14,7 +14,7 @@ Gem::Specification.new do |gem|
   gem.version       = "0.7.0"
   gem.license = 'MIT'
 
-  gem.add_runtime_dependency('activesupport', '~> 5.1')
+  gem.add_runtime_dependency('activesupport', '>= 5.1', '< 7')
   gem.add_development_dependency('rspec', '~> 3.7.0')
   gem.add_development_dependency('rake')