diff --git a/deface.gemspec b/deface.gemspec
index 72c413f..ed4c7cb 100644
--- a/deface.gemspec
+++ b/deface.gemspec
@@ -44,7 +44,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency('erubis')
   spec.add_development_dependency('gem-release')
   spec.add_development_dependency('rspec', '>= 3.1.0')
-  spec.add_development_dependency('haml', ['>= 4.0', '< 6'])
+  spec.add_development_dependency('haml', '>= 4.0', '< 7')
   spec.add_development_dependency('slim', '~> 4.1')
   spec.add_development_dependency('simplecov', '>= 0.6.4')
   spec.add_development_dependency('generator_spec', '~> 0.8')