foo.diff

diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index 63da28d..9452b06 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -617,9 +617,12 @@ class ReverseSingleRelatedObjectDescriptor(object):
             if related is not None:
                 setattr(related, self.field.related.get_cache_name(), None)
 
-        # Set the value of the related field
-        for lh_field, rh_field in self.field.related_fields:
-            try:
+            for lh_field, rh_field in self.field.related_fields:
+                setattr(instance, lh_field.attname, None)
+
+        # Set the values of the related field.
+        else:
+            for lh_field, rh_field in self.field.related_fields:
                 val = getattr(value, rh_field.attname)
                 if val is None:
                     raise ValueError(
@@ -627,8 +630,6 @@ class ReverseSingleRelatedObjectDescriptor(object):
                         (value, self.field.rel.to._meta.object_name)
                     )
                 setattr(instance, lh_field.attname, val)
-            except AttributeError:
-                setattr(instance, lh_field.attname, None)
 
         # Since we already know what the related object is, seed the related
         # object caches now, too. This avoids another db hit if you get the