diff --git a/django/db/models/base.py b/django/db/models/base.py
index af06ee1c12..06db7cc4e6 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -745,9 +745,7 @@ class Model(object):
             if not getattr(self, '_adding', False) and self.pk is not None:
                 qs = qs.exclude(pk=self.pk)
 
-            # This cute trick with extra/values is the most efficient way to
-            # tell if a particular query returns any results.
-            if qs.extra(select={'a': 1}).values('a').order_by():
+            if qs.exists():
                 errors.setdefault(field, []).append(
                     self.date_error_message(lookup_type, field, unique_for)
                 )