diff --git a/lib/pure/asyncfile.nim b/lib/pure/asyncfile.nim
index 382590478171..3a57845c2278 100644
--- a/lib/pure/asyncfile.nim
+++ b/lib/pure/asyncfile.nim
@@ -428,7 +428,7 @@ proc write*(f: AsyncFile, data: string): Future[void] =
           dealloc buffer
           buffer = nil
     )
-    ol.offset = DWORD(f.offset and 0xffffffff)
+    ol.offset = cast[DWORD](f.offset and 0xffffffff)
     ol.offsetHigh = DWORD(f.offset shr 32)
     f.offset.inc(data.len)