diff --git a/Gemfile b/Gemfile
index 636e844e6..7f20fa1ee 100644
--- a/Gemfile
+++ b/Gemfile
@@ -50,7 +50,7 @@ end
 # Optional CommonMark support, not for JRuby
 group :common_mark do
   gem "html-pipeline", "~> 2.13.2"
-  gem "commonmarker", (RUBY_VERSION < '2.6' ? '0.21.0' : '~> 0.22')
+  gem "commonmarker", (Gem.ruby_version < Gem::Version.new('2.6.0') ? '0.21.0' : '~> 0.22')
   gem "sanitize", "~> 6.0"
 end