diff --git a/nova/tests/virt/xenapi/test_vm_utils.py b/nova/tests/virt/xenapi/test_vm_utils.py
index 99bb2761f181..07769a6eb135 100644
--- a/nova/tests/virt/xenapi/test_vm_utils.py
+++ b/nova/tests/virt/xenapi/test_vm_utils.py
@@ -977,7 +977,7 @@ class GenerateDiskTestCase(VMUtilsTestBase):
             utils.execute('parted', '--script', '/dev/fakedev', 'mklabel',
                           'msdos', check_exit_code=False, run_as_root=True)
             utils.execute('parted', '--script', '/dev/fakedev', 'mkpart',
-                          'primary', '0', '10',
+                          'primary', '0', '-0',
                           check_exit_code=False, run_as_root=True)
             vm_utils.os.path.exists('/dev/mapper/fakedev1').AndReturn(True)
             utils.trycmd('kpartx', '-a', '/dev/fakedev',
@@ -986,7 +986,7 @@ class GenerateDiskTestCase(VMUtilsTestBase):
             utils.execute('parted', '--script', '/dev/fakedev', 'mklabel',
                           'msdos', check_exit_code=True, run_as_root=True)
             utils.execute('parted', '--script', '/dev/fakedev', 'mkpart',
-                          'primary', '0', '10',
+                          'primary', '0', '-0',
                           check_exit_code=True, run_as_root=True)
 
     def _check_vdi(self, vdi_ref):
diff --git a/nova/virt/xenapi/vm_utils.py b/nova/virt/xenapi/vm_utils.py
index 6371fb174177..50c02da42569 100644
--- a/nova/virt/xenapi/vm_utils.py
+++ b/nova/virt/xenapi/vm_utils.py
@@ -954,12 +954,11 @@ def _generate_disk(session, instance, vm_ref, userdevice, name_label,
         # 2. Attach VDI to compute worker (VBD hotplug)
         with vdi_attached_here(session, vdi_ref, read_only=False) as dev:
             # 3. Create partition
-            partition_start = 0
-            partition_end = size_mb
+            partition_start = "0"
+            partition_end = "-0"
 
             partition_path = _make_partition(session, dev,
-                                             "%d" % partition_start,
-                                             "%d" % partition_end)
+                                             partition_start, partition_end)
 
             if fs_type == 'linux-swap':
                 utils.execute('mkswap', partition_path, run_as_root=True)