diff --git a/lib/mjml/parser.rb b/lib/mjml/parser.rb
index a2bb958..b93ddad 100644
--- a/lib/mjml/parser.rb
+++ b/lib/mjml/parser.rb
@@ -45,7 +45,7 @@ def exec!
     end
 
     def partial?
-      (@template =~ ROOT_TAGS_REGEX).nil?
+      (@template.to_s =~ ROOT_TAGS_REGEX).nil?
     end
 
     def mjml_bin