diff --git a/lib/chartkick/helper.rb b/lib/chartkick/helper.rb
index 9f16bec..fb7a25d 100644
--- a/lib/chartkick/helper.rb
+++ b/lib/chartkick/helper.rb
@@ -78,7 +78,7 @@ def chartkick_chart(klass, data_source, **options)
         # limit to alphanumeric and % for simplicity
         # this prevents things like calc() but safety is the priority
         # dot does not need escaped in square brackets
-        raise ArgumentError, "Invalid #{k}" unless html_vars[k] =~ /\A[a-zA-Z0-9%.]*\z/
+        raise ArgumentError, "Invalid #{k}" unless /\A[a-zA-Z0-9%.]*\z/.match?(html_vars[k])
       end
 
       html_vars.each_key do |k|