diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 4f5b157af9122832e7ca40898e007124cf0ad383..17662592ad25751ccab9427ed32246f56e0173d4 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -79,10 +79,7 @@ def build_relation(klass, attribute, value)
         else
           klass.connection.case_sensitive_comparison(table, attribute, column, value)
         end
-        klass.unscoped.tap do |scope|
-          parts = [comparison]
-          scope.where_clause += Relation::WhereClause.new(parts)
-        end
+        klass.unscoped.where!(comparison)
       end
 
       def scope_relation(record, relation)