diff --git a/libvncserver/tightvnc-filetransfer/filetransfermsg.c b/libvncserver/tightvnc-filetransfer/filetransfermsg.c
index 7dae2cd..a0d7a5e 100644
--- a/libvncserver/tightvnc-filetransfer/filetransfermsg.c
+++ b/libvncserver/tightvnc-filetransfer/filetransfermsg.c
@@ -393,7 +393,7 @@ FileTransferMsg
 CreateFileDownloadZeroSizeDataMsg(unsigned long mTime)
 {
 	FileTransferMsg fileDownloadZeroSizeDataMsg;
-	int length = sz_rfbFileDownloadDataMsg + sizeof(int);
+	int length = sz_rfbFileDownloadDataMsg + sizeof(unsigned long);
 	rfbFileDownloadDataMsg *pFDD = NULL;
 	char *pFollow = NULL;