diff --git a/dlls/ntdll/file.c b/dlls/ntdll/file.c
index 12ece05fae1..3889fc7c4cb 100644
--- a/dlls/ntdll/file.c
+++ b/dlls/ntdll/file.c
@@ -558,8 +558,12 @@ NTSTATUS WINAPI NtWriteFile(HANDLE hFile, HANDLE hEvent,
         ovp->async.event = hEvent;
         ovp->async.iosb = io_status;
         ovp->count = length;
-        ovp->offset = offset->s.LowPart;
-        if (offset->s.HighPart) FIXME("NIY-high part\n");
+        if (offset) {
+            ovp->offset = offset->s.LowPart;
+            if (offset->s.HighPart) FIXME("NIY-high part\n");
+        } else {
+            ovp->offset = 0;
+        }
         ovp->apc = apc;
         ovp->apc_user = apc_user;
         ovp->buffer = (void*)buffer;