diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index a69cc5ac8c..a97adef474 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -326,7 +326,7 @@ class Field(object):
             params['validator_list'].append(getattr(manipulator, 'isUnique%sFor%s' % (self.name, self.unique_for_month)))
         if self.unique_for_year:
             params['validator_list'].append(getattr(manipulator, 'isUnique%sFor%s' % (self.name, self.unique_for_year)))
-        if self.unique or (self.primary_key and not rel):
+        if self.unique and not rel:
             params['validator_list'].append(curry(manipulator_validator_unique, self, opts, manipulator))
 
         # Only add is_required=True if the field cannot be blank. Primary keys