diff --git a/django/core/management/validation.py b/django/core/management/validation.py
index 55665804c4..c13b19df97 100644
--- a/django/core/management/validation.py
+++ b/django/core/management/validation.py
@@ -39,6 +39,8 @@ def get_validation_errors(outfile, app=None):
                 e.add(opts, '"%s": You can\'t use "id" as a field name, because each model automatically gets an "id" field if none of the fields have primary_key=True. You need to either remove/rename your "id" field or add primary_key=True to a field.' % f.name)
             if f.name.endswith('_'):
                 e.add(opts, '"%s": Field names cannot end with underscores, because this would lead to ambiguous queryset filters.' % f.name)
+            if f.primary_key and f.null:
+                e.add(opts, '"%s": Primary key fields cannot have null=True.' % f.name)
             if isinstance(f, models.CharField):
                 try:
                     max_length = int(f.max_length)
diff --git a/tests/modeltests/invalid_models/invalid_models/models.py b/tests/modeltests/invalid_models/invalid_models/models.py
index e32ff04ea8..e549478496 100644
--- a/tests/modeltests/invalid_models/invalid_models/models.py
+++ b/tests/modeltests/invalid_models/invalid_models/models.py
@@ -220,7 +220,8 @@ class InvalidSetDefault(models.Model):
     fk = models.ForeignKey('self', on_delete=models.SET_DEFAULT)
 
 class UnicodeForeignKeys(models.Model):
-    """Foreign keys which can translate to ascii should be OK, but fail if they're not."""
+    """Foreign keys which can translate to ascii should be OK, but fail if
+    they're not."""
     good = models.ForeignKey(u'FKTarget')
     also_good = models.ManyToManyField(u'FKTarget', related_name='unicode2')
 
@@ -228,6 +229,9 @@ class UnicodeForeignKeys(models.Model):
     # when adding the errors in core/management/validation.py
     #bad = models.ForeignKey(u'★')
 
+class PrimaryKeyNull(models.Model):
+    my_pk_field = models.IntegerField(primary_key=True, null=True)
+
 
 model_errors = """invalid_models.fielderrors: "charfield": CharFields require a "max_length" attribute that is a positive integer.
 invalid_models.fielderrors: "charfield2": CharFields require a "max_length" attribute that is a positive integer.
@@ -338,4 +342,5 @@ invalid_models.nonuniquefktarget2: Field 'bad' under model 'FKTarget' must have
 invalid_models.nonexistingorderingwithsingleunderscore: "ordering" refers to "does_not_exist", a field that doesn't exist.
 invalid_models.invalidsetnull: 'fk' specifies on_delete=SET_NULL, but cannot be null.
 invalid_models.invalidsetdefault: 'fk' specifies on_delete=SET_DEFAULT, but has no default value.
+invalid_models.primarykeynull: "my_pk_field": Primary key fields cannot have null=True.
 """