diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index c41d4ea..1c24c7c 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -1400,9 +1400,11 @@ class DateTimeField(DateField):
             # For backwards compatibility, interpret naive datetimes in local
             # time. This won't work during DST change, but we can't do much
             # about it, so we let the exceptions percolate up the call stack.
-            warnings.warn("DateTimeField %s.%s received a naive datetime (%s)"
+            name = '%s.%s' % (self.model.__name__, self.name) \
+                if hasattr(self, 'model') else '(unbound)'
+            warnings.warn("DateTimeField %s received a naive datetime (%s)"
                           " while time zone support is active." %
-                          (self.model.__name__, self.name, value),
+                          (name, value),
                           RuntimeWarning)
             default_timezone = timezone.get_default_timezone()
             value = timezone.make_aware(value, default_timezone)