diff --git a/artiq-fast/windows/win.nix b/artiq-fast/windows/win.nix
index 6d57a29..75956cb 100644
--- a/artiq-fast/windows/win.nix
+++ b/artiq-fast/windows/win.nix
@@ -6,6 +6,7 @@
 , autoUnattendParams ? {}
 , packages ? []
 , impureMode ? false
+, baseRtc ? "2020-04-20T14:21:42"
 , ...
 }@attrs:
 
@@ -145,6 +146,8 @@ let
         "usb-storage,drive=virtio-win"
         # "CD" drive with windows features-on-demand
         # "-cdrom" "${fodIso}"
+        # Set the base clock inside the VM
+        "-rtc=$(date -Iseconds -d @${baseRtc}"
       ] ++ lib.optional (!impureMode) "-nographic";
     in
       ''