diff --git a/tests/integration/test_openvixdisklib.py b/tests/integration/test_openvixdisklib.py
index 5212170..08b8a33 100644
--- a/tests/integration/test_openvixdisklib.py
+++ b/tests/integration/test_openvixdisklib.py
@@ -3,11 +3,34 @@
 
 """Exercise the VDDK-compatible openvixdisklib handle against the lab."""
 
+from pyVim.connect import Disconnect
+from pyVmomi import vim
 import pytest
 
+from openvixdisklib import nfc_auth
 from openvixdisklib import openvixdisklib as vixdisklib
 from tests.integration.base import (
-    LabEnv, SECTOR_AT_1GB, SECTOR_SIZE, pattern_bytes)
+    LabEnv, SECTOR_AT_1GB, SECTOR_SIZE, _wait_for_task, pattern_bytes)
+
+
+def _connect_lab_vim(lab: LabEnv) -> vim.ServiceInstance:
+    """Login to the lab vCenter with the session VM's credentials."""
+    return nfc_auth.connect_vim(
+        lab.host,
+        lab.username,
+        lab.password,
+        port=lab.port,
+        thumbprint=lab.thumbprint,
+        allow_untrusted=lab.allow_untrusted)
+
+
+def _virtual_disk_backing(
+        vm: vim.VirtualMachine) -> vim.vm.device.VirtualDevice.BackingInfo:
+    """Return the lab VM's first virtual disk backing."""
+    for device in vm.config.hardware.device:
+        if isinstance(device, vim.vm.device.VirtualDisk):
+            return device.backing
+    raise AssertionError(f"{vm._moId} has no virtual disk")
 
 
 class TestOpenvixdisklib:
@@ -42,3 +65,58 @@ class TestOpenvixdisklib:
                     read_buf[:SECTOR_SIZE] = b"\xa5" * SECTOR_SIZE
                     handle.read(disk, start, 1, read_buf)
                     assert read_buf.raw[:SECTOR_SIZE] == expected
+
+    def test_read_only_open_snapshot_parent(self, lab: LabEnv) -> None:
+        """Read-only Open uses NfcGetVmFiles, including a snapshot parent path.
+
+        After a snapshot the attached leaf is a new delta (``…-000001.vmdk``)
+        while backup tools open the parent file. That path is not
+        ``device.backing.fileName``; VDDK still opens it with a VM-only
+        ticket and NFC ``OPEN_FILE``.
+        """
+        handle = vixdisklib.VixDiskLibHandle(
+            vixdisklib_compatibility_version="8.0")
+        expected = pattern_bytes(SECTOR_SIZE, b"OVDL-RO")
+        write_buf = vixdisklib.get_buffer(SECTOR_SIZE)
+        read_buf = vixdisklib.get_buffer(SECTOR_SIZE)
+        write_buf[:SECTOR_SIZE] = expected
+        write_kwargs = lab.vixdisklib_connect_kwargs({
+            "allow_untrusted": lab.allow_untrusted,
+        })
+        read_kwargs = lab.vixdisklib_connect_kwargs({
+            "allow_untrusted": lab.allow_untrusted,
+            "read_only": True,
+        })
+        read_flags = vixdisklib.VIXDISKLIB_FLAG_OPEN_READ_ONLY
+
+        def read_sector(path: str) -> bytes:
+            with handle.connect(**read_kwargs) as conn:
+                with handle.open(conn, path, flags=read_flags) as disk:
+                    read_buf[:SECTOR_SIZE] = b"\xa5" * SECTOR_SIZE
+                    handle.read(disk, 0, 1, read_buf)
+            return read_buf.raw[:SECTOR_SIZE]
+
+        with handle.connect(**write_kwargs) as conn:
+            with handle.open(conn, lab.disk_path, flags=0) as disk:
+                handle.write(disk, 0, 1, write_buf)
+
+        assert read_sector(lab.disk_path) == expected
+
+        si = _connect_lab_vim(lab)
+        try:
+            vm = vim.VirtualMachine(lab.vm_moref, si._stub)
+            _wait_for_task(
+                vm.CreateSnapshot_Task("ovdl-readonly", "", False, False))
+            backing = _virtual_disk_backing(vm)
+            parent = getattr(backing, "parent", None)
+            assert parent is not None
+            assert parent.fileName == lab.disk_path
+            assert backing.fileName != parent.fileName
+            assert read_sector(parent.fileName) == expected
+        finally:
+            try:
+                vm = vim.VirtualMachine(lab.vm_moref, si._stub)
+                if vm.snapshot is not None:
+                    _wait_for_task(vm.RemoveAllSnapshots_Task())
+            finally:
+                Disconnect(si)