diff --git a/schema_plus_core.gemspec b/schema_plus_core.gemspec
index beca631..4e46134 100644
--- a/schema_plus_core.gemspec
+++ b/schema_plus_core.gemspec
@@ -18,7 +18,7 @@ Gem::Specification.new do |gem|
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
   gem.require_paths = ["lib"]
 
-  gem.add_dependency "activerecord", ">= 4.2"
+  gem.add_dependency "activerecord", ">= 4.2", "< 6"
   gem.add_dependency "schema_monkey", "~> 2.1"
 
   gem.add_development_dependency "bundler", "~> 1.7"