diff --git a/django/contrib/admin/templatetags/admin_list.py b/django/contrib/admin/templatetags/admin_list.py
index 21e87f572b..93e9b0799b 100644
--- a/django/contrib/admin/templatetags/admin_list.py
+++ b/django/contrib/admin/templatetags/admin_list.py
@@ -116,11 +116,7 @@ def result_headers(cl):
             # So this _is_ a sortable non-field.  Go to the yield
             # after the else clause.
         else:
-            if isinstance(f.rel, models.ManyToOneRel) and f.null:
-                yield {"text": f.verbose_name}
-                continue
-            else:
-                header = f.verbose_name
+            header = f.verbose_name
 
         th_classes = []
         new_order_type = 'asc'
diff --git a/django/contrib/admin/views/main.py b/django/contrib/admin/views/main.py
index a6a206d1dc..bcfa3a8155 100644
--- a/django/contrib/admin/views/main.py
+++ b/django/contrib/admin/views/main.py
@@ -162,8 +162,7 @@ class ChangeList(object):
                     except AttributeError:
                         pass
                 else:
-                    if not isinstance(f.rel, models.ManyToOneRel) or not f.null:
-                        order_field = f.name
+                    order_field = f.name
             except (IndexError, ValueError):
                 pass # Invalid ordering specified. Just use the default.
         if ORDER_TYPE_VAR in params and params[ORDER_TYPE_VAR] in ('asc', 'desc'):