diff --git a/ntoskrnl/io/pnpmgr/pnpmgr.c b/ntoskrnl/io/pnpmgr/pnpmgr.c
index b4f59f4d17e..e5530c61714 100644
--- a/ntoskrnl/io/pnpmgr/pnpmgr.c
+++ b/ntoskrnl/io/pnpmgr/pnpmgr.c
@@ -1853,7 +1853,7 @@ IopGetParentIdPrefix(PDEVICE_NODE DeviceNode,
     }
 
     /* 1. Try to retrieve ParentIdPrefix from registry */
-    KeyNameBufferLength = FIELD_OFFSET(KEY_VALUE_PARTIAL_INFORMATION, Data[0]) + MAX_PATH * sizeof(WCHAR);
+    KeyNameBufferLength = FIELD_OFFSET(KEY_VALUE_PARTIAL_INFORMATION, Data) + sizeof(L"12345678&12345678");
     ParentIdPrefixInformation = ExAllocatePoolWithTag(PagedPool,
                                                       KeyNameBufferLength + sizeof(UNICODE_NULL),
                                                       TAG_IO);