diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 9bb45aa3b7..ae1c326d95 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -479,7 +479,7 @@ module ActiveRecord
 
         clear_attribute_changes(changes.keys)
         primary_key = self.class.primary_key
-        scope = self.class.unscoped.where(primary_key => id)
+        scope = self.class.unscoped.where(primary_key => _read_attribute(primary_key))
 
         if locking_enabled?
           locking_column = self.class.locking_column