diff --git a/django/db/models/base.py b/django/db/models/base.py
index f29d7db629..27117742eb 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -263,7 +263,7 @@ class ModelState(object):
         # If true, uniqueness validation checks will consider this a new, as-yet-unsaved object.
         # Necessary for correct validation of new instances of objects with explicit (non-auto) PKs.
         # This impacts validation only; it has no effect on the actual save.
-        self.adding = False
+        self.adding = True
 
 class Model(object):
     __metaclass__ = ModelBase
diff --git a/django/db/models/query.py b/django/db/models/query.py
index 2c679b04a6..b150d0cce1 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -282,6 +282,8 @@ class QuerySet(object):
 
                 # Store the source database of the object
                 obj._state.db = self.db
+                # This object came from the database; it's not being added.
+                obj._state.adding = False
 
             for i, k in enumerate(extra_select):
                 setattr(obj, k, row[i])
@@ -1220,6 +1222,7 @@ def get_cached_row(klass, row, index_start, using, max_depth=0, cur_depth=0,
     # If an object was retrieved, set the database state.
     if obj:
         obj._state.db = using
+        obj._state.adding = False
 
     index_end = index_start + field_count + offset
     # Iterate over each related object, populating any
@@ -1475,6 +1478,7 @@ class RawQuerySet(object):
             setattr(instance, field, value)
 
         instance._state.db = self.query.using
+        instance._state.adding = False
 
         return instance
 
diff --git a/django/forms/models.py b/django/forms/models.py
index c5be8aa1e3..6ba2bed472 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -244,10 +244,8 @@ class BaseModelForm(BaseForm):
             # if we didn't get an instance, instantiate a new one
             self.instance = opts.model()
             object_data = {}
-            self.instance._state.adding = True
         else:
             self.instance = instance
-            self.instance._state.adding = False
             object_data = model_to_dict(instance, opts.fields, opts.exclude)
         # if initial was provided, it should override the values from instance
         if initial is not None:
diff --git a/tests/regressiontests/model_regress/models.py b/tests/regressiontests/model_regress/models.py
index 420f2c262c..6c5d7bd59e 100644
--- a/tests/regressiontests/model_regress/models.py
+++ b/tests/regressiontests/model_regress/models.py
@@ -58,6 +58,8 @@ class BrokenUnicodeMethod(models.Model):
         # object).
         return 'Názov: %s' % self.name
 
+class NonAutoPK(models.Model):
+    name = models.CharField(max_length=10, primary_key=True)
 
 __test__ = {'API_TESTS': """
 (NOTE: Part of the regression test here is merely parsing the model
diff --git a/tests/regressiontests/model_regress/tests.py b/tests/regressiontests/model_regress/tests.py
index 0257c63d8c..6397b90a66 100644
--- a/tests/regressiontests/model_regress/tests.py
+++ b/tests/regressiontests/model_regress/tests.py
@@ -1,16 +1,26 @@
-from models import Worker
+from django.core.exceptions import ValidationError
 from django.test import TestCase
 
+from models import Worker, NonAutoPK
+
+
 class RelatedModelOrderedLookupTest(TestCase):
     """
     Regression test for #10153: foreign key __gte and __lte lookups.
     """
-    
+
     # The bug is that the following queries would raise:
     # "TypeError: Related Field has invalid lookup: gte"
-    
+
     def test_related_gte_lookup(self):
         Worker.objects.filter(department__gte=0)
 
     def test_related_lte_lookup(self):
         Worker.objects.filter(department__lte=0)
+
+
+class ModelValidationTest(TestCase):
+    def test_pk_validation(self):
+        one = NonAutoPK.objects.create(name="one")
+        again = NonAutoPK(name="one")
+        self.assertRaises(ValidationError, again.validate_unique)