diff --git a/lib/has_permalink.rb b/lib/has_permalink.rb
index 6c9d9a3..8b1f127 100644
--- a/lib/has_permalink.rb
+++ b/lib/has_permalink.rb
@@ -53,10 +53,10 @@ def to_param
     # Autofix duplication of permalinks
     def fix_duplication(permalink)
       if auto_fix_duplication
-        n = self.class.where(["permalink = ?", permalink]).count
+        n = self.class.base_class.where(["permalink = ?", permalink]).count
 
         if n > 0
-          links = self.class.where(["permalink LIKE ?", "#{permalink}%"]).order("id")
+          links = self.class.base_class.where(["permalink LIKE ?", "#{permalink}%"]).order("id")
 
           number = 0