foo.diff

diff --git a/django/db/models/query.py b/django/db/models/query.py
index ef0c2db..20edcd6 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -886,16 +886,14 @@ class QuerySet(object):
         if names is None:
             names = {f.name for f in self.model._meta.get_fields()}
 
+        added_aggregates = False
         for alias, annotation in annotations.items():
             if alias in names:
                 raise ValueError("The annotation '%s' conflicts with a field on "
                                  "the model." % alias)
             clone.query.add_annotation(annotation, alias, is_summary=False)
-
-        added_aggregates = []
-        for alias, annotation in clone.query.annotations.items():
-            if alias in annotations and annotation.contains_aggregate:
-                added_aggregates.append(alias)
+            if annotation.contains_aggregate:
+                added_aggregates = True
 
         if added_aggregates:
             if clone._fields is None: