diff --git a/rtl/unix/dos.pp b/rtl/unix/dos.pp
index 7d6858a0d8..995a677a64 100644
--- a/rtl/unix/dos.pp
+++ b/rtl/unix/dos.pp
@@ -297,7 +297,7 @@ var
 {  tz : TimeZone;}
 begin
   FPGetTimeOfDay (@tv, nil {,tz});
-  GetMsCount := tv.tv_Sec * 1000 + tv.tv_uSec div 1000;
+  GetMsCount := int64(tv.tv_Sec) * 1000 + tv.tv_uSec div 1000;
 end;