diff --git a/nova/tests/virt/xenapi/test_vmops.py b/nova/tests/virt/xenapi/test_vmops.py
index 7283179d70b4..200a6c0c681f 100644
--- a/nova/tests/virt/xenapi/test_vmops.py
+++ b/nova/tests/virt/xenapi/test_vmops.py
@@ -850,6 +850,14 @@ class ResizeVdisTestCase(VMOpsTestBase):
         self.vmops._resize_up_vdis(instance, {"root": {}})
         self.assertFalse(mock_resize.called)
 
+    def test_resize_up_vdis_no_vdis_like_initial_spawn(self, mock_resize):
+        instance = {"root_gb": 0, "ephemeral_gb": 3000}
+        vdis = {}
+
+        self.vmops._resize_up_vdis(instance, vdis)
+
+        self.assertFalse(mock_resize.called)
+
     @mock.patch.object(vm_utils, 'get_ephemeral_disk_sizes')
     def test_resize_up_vdis_ephemeral(self, mock_sizes, mock_resize):
         mock_sizes.return_value = [2000, 1000]
diff --git a/nova/virt/xenapi/vmops.py b/nova/virt/xenapi/vmops.py
index 15397aeb84aa..c215df8b3666 100644
--- a/nova/virt/xenapi/vmops.py
+++ b/nova/virt/xenapi/vmops.py
@@ -1080,10 +1080,18 @@ class VMOps(object):
             vm_utils.update_vdi_virtual_size(self._session, instance,
                                              vdi_ref, new_root_gb)
 
+        ephemeral_vdis = vdis.get('ephemerals')
+        if not ephemeral_vdis:
+            # NOTE(johngarbutt) no existing (migrated) ephemeral disks
+            # to resize, so nothing more to do here.
+            return
+
         total_ephemeral_gb = instance['ephemeral_gb']
         if total_ephemeral_gb:
             sizes = vm_utils.get_ephemeral_disk_sizes(total_ephemeral_gb)
-            ephemeral_vdis = vdis.get('ephemerals')
+            # resize existing (migrated) ephemeral disks,
+            # and add any extra disks if required due to a
+            # larger total_ephemeral_gb (resize down is not supported).
             for userdevice, new_size in enumerate(sizes,
                                                   start=int(DEVICE_EPHEMERAL)):
                 vdi = ephemeral_vdis.get(str(userdevice))