diff --git a/django/core/management/commands/dumpdata.py b/django/core/management/commands/dumpdata.py
index b1e06e4255..c5eb1b9a9e 100644
--- a/django/core/management/commands/dumpdata.py
+++ b/django/core/management/commands/dumpdata.py
@@ -21,8 +21,9 @@ class Command(BaseCommand):
             help='Use natural keys if they are available.'),
         make_option('-a', '--all', action='store_true', dest='use_base_manager', default=False,
             help="Use Django's base manager to dump all models stored in the database, including those that would otherwise be filtered or modified by a custom manager."),
-        make_option('--pks', dest='primary_keys', action='append', default=[],
-            help="Only dump objects with given primary keys. Accepts a comma seperated list of keys. This option will only work when you specify one model."),
+        make_option('--pks', dest='primary_keys', help="Only dump objects with "
+            "given primary keys. Accepts a comma seperated list of keys. "
+            "This option will only work when you specify one model."),
     )
     help = ("Output the contents of the database as a fixture of the given "
             "format (using each model's default manager unless --all is "
@@ -44,7 +45,7 @@ class Command(BaseCommand):
         if pks:
             primary_keys = pks.split(',')
         else:
-            primary_keys = False
+            primary_keys = []
 
         excluded_apps = set()
         excluded_models = set()
diff --git a/tests/admin_scripts/tests.py b/tests/admin_scripts/tests.py
index f0ef0fb293..9e6b1f557b 100644
--- a/tests/admin_scripts/tests.py
+++ b/tests/admin_scripts/tests.py
@@ -1682,3 +1682,22 @@ class DiffSettings(AdminScriptTestCase):
         out, err = self.run_manage(args)
         self.assertNoOutput(err)
         self.assertOutput(out, "### STATIC_URL = None")
+
+class Dumpdata(AdminScriptTestCase):
+    """Tests for dumpdata management command."""
+
+    def setUp(self):
+        self.write_settings('settings.py')
+
+    def tearDown(self):
+        self.remove_settings('settings.py')
+
+    def test_pks_parsing(self):
+        """Regression for #20509
+
+        Test would raise an exception rather than printing an error message.
+        """
+        args = ['dumpdata', '--pks=1']
+        out, err = self.run_manage(args)
+        self.assertOutput(err, "You can only use --pks option with one model")
+        self.assertNoOutput(out)
diff --git a/tests/fixtures/tests.py b/tests/fixtures/tests.py
index 4bf60e988a..1b4d6eeeef 100644
--- a/tests/fixtures/tests.py
+++ b/tests/fixtures/tests.py
@@ -27,7 +27,7 @@ class TestCaseFixtureLoadingTests(TestCase):
 class DumpDataAssertMixin(object):
 
     def _dumpdata_assert(self, args, output, format='json', natural_keys=False,
-                         use_base_manager=False, exclude_list=[], primary_keys=[]):
+                         use_base_manager=False, exclude_list=[], primary_keys=''):
         new_io = six.StringIO()
         management.call_command('dumpdata', *args, **{'format': format,
                                                       'stdout': new_io,