diff --git a/instances/test_disk_isolation.py b/instances/test_disk_isolation.py
index ae03b011..951551a8 100644
--- a/instances/test_disk_isolation.py
+++ b/instances/test_disk_isolation.py
@@ -304,3 +304,14 @@ class DiskViewsTenantIsolationTestCase(TestCase):
                  "bus": "virtio", "cache": "default"},
             )
         mock_create.return_value.create_volume.assert_not_called()
+
+    def test_edit_volume_accepts_a_disk_without_any_driver_format(self):
+        self.client.force_login(self.superuser)
+        no_format_disk = dict(VM_DISK, format=None)
+        with patch("instances.models.wvmInstance") as mock_wvm:
+            proxy = mock_wvm.return_value
+            self._mock_disk_options(proxy)
+            proxy.get_disk_devices.return_value = [no_format_disk]
+            self._edit_volume_post(vol_format="None")
+        proxy.edit_disk.assert_called_once()
+        self.assertEqual(proxy.edit_disk.call_args[0][6], "")
diff --git a/instances/views.py b/instances/views.py
index 1813238f..75c85eee 100755
--- a/instances/views.py
+++ b/instances/views.py
@@ -985,7 +985,8 @@ def edit_volume(request, pk):
             io=io,
             discard=discard,
             zeroes=zeroes,
-            format=format,
+            # "": the disk has no driver type and keeps having none.
+            format=format or None,
             serial=serial,
         )
         if target_dev not in [disk["dev"] for disk in instance.disks]:
diff --git a/vrtManager/instance.py b/vrtManager/instance.py
index cf5162a1..6c418d7d 100644
--- a/vrtManager/instance.py
+++ b/vrtManager/instance.py
@@ -913,12 +913,12 @@ class wvmInstance(wvmConnect):
             additionals += f"detect_zeroes='{detect_zeroes_mode}' "
 
         xml_disk = f"<disk type='{old_disk_type}' device='{old_disk_device}'>"
+        # A disk without a driver type keeps having none.
+        type_attr = f"type='{format}' " if format else ""
         if old_disk_device == "cdrom":
-            xml_disk += f"<driver name='{old_driver_name}' type='{format}'/>"
+            xml_disk += f"<driver name='{old_driver_name}' {type_attr}/>"
         elif old_disk_device == "disk":
-            xml_disk += (
-                f"<driver name='{old_driver_name}' type='{format}' {additionals}/>"
-            )
+            xml_disk += f"<driver name='{old_driver_name}' {type_attr}{additionals}/>"
 
         if disk_el.get("type") == "file":
             xml_disk += f"<source file='{source}'/>"
diff --git a/vrtManager/test_xml_safety.py b/vrtManager/test_xml_safety.py
index 32b1369a..91d3ac13 100644
--- a/vrtManager/test_xml_safety.py
+++ b/vrtManager/test_xml_safety.py
@@ -304,3 +304,22 @@ class TestChangeDiskBus(unittest.TestCase):
         self.assertEqual(disk.find("source").get("name"), "pool/vm-disk")
         self.assertEqual(disk.find("source/host").get("name"), "mon1")
         self.assertEqual(disk.find("auth/secret").get("uuid"), "aaaa")
+
+    def test_edit_disk_without_format_omits_the_driver_type(self):
+        from lxml import etree
+
+        inst = wvmInstance.__new__(wvmInstance)
+        inst.instance = MagicMock()
+        inst._XMLDesc = MagicMock(
+            return_value=(
+                "<domain><devices><disk type='file' device='disk'>"
+                "<driver name='qemu'/><source file='/images/vm.img'/>"
+                "<target dev='vda' bus='virtio'/></disk></devices></domain>"
+            )
+        )
+        inst.edit_disk(
+            "vda", "/images/vm.img", False, False, "virtio", "", "",
+            "default", "default", "default", "default",
+        )
+        disk = etree.fromstring(inst.instance.updateDeviceFlags.call_args[0][0])
+        self.assertIsNone(disk.find("driver").get("type"))