diff --git a/middleman-core/middleman-core.gemspec b/middleman-core/middleman-core.gemspec
index 81f7712a..9e50403b 100644
--- a/middleman-core/middleman-core.gemspec
+++ b/middleman-core/middleman-core.gemspec
@@ -29,7 +29,7 @@ Gem::Specification.new do |s|
   s.add_dependency('dotenv')
 
   # Helpers
-  s.add_dependency('activesupport', ['~> 5.0'])
+  s.add_dependency('activesupport', ['>= 4.2', '< 5.1'])
   s.add_dependency('padrino-helpers', ['~> 0.13.0'])
   s.add_dependency("addressable", ["~> 2.3"])
   s.add_dependency('memoist', ['~> 0.14'])