diff --git a/lib/psych/visitors/yaml_tree.rb b/lib/psych/visitors/yaml_tree.rb
index b6c86f4c..0fb2714a 100644
--- a/lib/psych/visitors/yaml_tree.rb
+++ b/lib/psych/visitors/yaml_tree.rb
@@ -607,7 +607,8 @@ def accept target
           raise BadAlias, "Tried to dump an aliased object"
         end
 
-        unless Symbol === target || @permitted_classes[target.class]
+        unless Symbol === target || @permitted_classes[target.class] ||
+            @permitted_classes.keys.include?(target.class.name)
           raise DisallowedClass.new('dump', target.class.name || target.class.inspect)
         end