diff --git a/nova/compute/api.py b/nova/compute/api.py
index 6cd25fecedf1..552d4c367b59 100644
--- a/nova/compute/api.py
+++ b/nova/compute/api.py
@@ -28,6 +28,7 @@ import string
 
 from oslo_log import log as logging
 from oslo_messaging import exceptions as oslo_exceptions
+from oslo_serialization import base64 as base64utils
 from oslo_serialization import jsonutils
 from oslo_utils import excutils
 from oslo_utils import strutils
@@ -832,7 +833,13 @@ class API(base.Base):
                     length=l, maxsize=MAX_USERDATA_SIZE)
 
             try:
-                base64.decodestring(user_data)
+                # TODO(gcb): Just use base64utils.decode_as_bytes(user_data)
+                # when https://review.openstack.org/#/c/410797/ is merged and
+                # ensure oslo.serialization >=2.15.0 in Nova requirements.txt.
+                if six.PY3:
+                    base64utils.decode_as_bytes(user_data)
+                else:
+                    base64.decodestring(user_data)
             except base64.binascii.Error:
                 raise exception.InstanceUserDataMalformed()
 
diff --git a/nova/tests/unit/compute/test_compute.py b/nova/tests/unit/compute/test_compute.py
index 605782d1b3ca..292c370fff03 100644
--- a/nova/tests/unit/compute/test_compute.py
+++ b/nova/tests/unit/compute/test_compute.py
@@ -17,7 +17,6 @@
 #    under the License.
 """Tests for compute service."""
 
-import base64
 import datetime
 import operator
 import sys
@@ -30,6 +29,7 @@ import mock
 from neutronclient.common import exceptions as neutron_exceptions
 from oslo_log import log as logging
 import oslo_messaging as messaging
+from oslo_serialization import base64
 from oslo_serialization import jsonutils
 from oslo_utils import fixture as utils_fixture
 from oslo_utils import timeutils
@@ -2739,7 +2739,7 @@ class ComputeTestCase(BaseTestCase):
     def test_rebuild_with_injected_files(self):
         # Ensure instance can be rebuilt with injected files.
         injected_files = [
-            (b'/a/b/c', base64.b64encode(b'foobarbaz')),
+            (b'/a/b/c', base64.encode_as_bytes(b'foobarbaz')),
         ]
 
         self.decoded_files = [
@@ -7939,7 +7939,7 @@ class ComputeAPITestCase(BaseTestCase):
         # base64
         (refs, resv_id) = self.compute_api.create(
             self.context, inst_type, self.fake_image['id'],
-            user_data=base64.encodestring(b'1' * 48510))
+            user_data=base64.encode_as_text(b'1' * 48510))
 
     def test_populate_instance_for_create(self, num_instances=1):
         base_options = {'image_ref': self.fake_image['id'],
@@ -11704,8 +11704,8 @@ class ComputeInjectedFilesTestCase(BaseTestCase):
     def test_injected_success(self):
         # test with valid b64 encoded content.
         injected_files = [
-            ('/a/b/c', base64.b64encode(b'foobarbaz')),
-            ('/d/e/f', base64.b64encode(b'seespotrun')),
+            ('/a/b/c', base64.encode_as_bytes(b'foobarbaz')),
+            ('/d/e/f', base64.encode_as_bytes(b'seespotrun')),
         ]
 
         decoded_files = [
@@ -11717,7 +11717,7 @@ class ComputeInjectedFilesTestCase(BaseTestCase):
     def test_injected_invalid(self):
         # test with invalid b64 encoded content
         injected_files = [
-            ('/a/b/c', base64.b64encode(b'foobarbaz')),
+            ('/a/b/c', base64.encode_as_bytes(b'foobarbaz')),
             ('/d/e/f', 'seespotrun'),
         ]
 
diff --git a/tests-py3.txt b/tests-py3.txt
index 412645e88766..388e79994773 100644
--- a/tests-py3.txt
+++ b/tests-py3.txt
@@ -5,10 +5,6 @@ nova.tests.unit.api.openstack.compute.test_security_group_default_rules.TestSecu
 nova.tests.unit.api.openstack.compute.test_security_groups.SecurityGroupsOutputTestV21
 nova.tests.unit.api.openstack.compute.test_security_groups.TestSecurityGroupRulesV21
 nova.tests.unit.api.openstack.compute.test_user_data.ServersControllerCreateTest
-nova.tests.unit.compute.test_compute.ComputeAPITestCase.test_create_with_base64_user_data
-nova.tests.unit.compute.test_compute_cells.CellsComputeAPITestCase.test_create_with_base64_user_data
-nova.tests.unit.compute.test_compute_mgr.ComputeManagerUnitTestCase.test_run_pending_deletes
-nova.tests.unit.compute.test_host_api.ComputeHostAPICellsTestCase
 nova.tests.unit.test_wsgi.TestWSGIServerWithSSL
 nova.tests.unit.virt.libvirt.test_firewall.IptablesFirewallTestCase
 nova.tests.unit.virt.libvirt.test_imagebackend.EncryptedLvmTestCase