diff --git a/rails_lti2_provider.gemspec b/rails_lti2_provider.gemspec
index 81f48d9..db0d37d 100644
--- a/rails_lti2_provider.gemspec
+++ b/rails_lti2_provider.gemspec
@@ -17,6 +17,7 @@ Gem::Specification.new do |s|
 
   s.files = Dir['{app,config,db,lib}/**/*', 'MIT-LICENSE', 'Rakefile', 'README.rdoc']
 
+  s.add_dependency('ims-lti', '~> 2.3.2.1')
   s.add_dependency('rails', '~> 6.0.3')
 
   s.add_development_dependency('rspec-rails', '~> 4.0')