diff --git a/artiq-fast/wfvm/utils.nix b/artiq-fast/wfvm/utils.nix
index 4a7ab9f..5f3e0d8 100644
--- a/artiq-fast/wfvm/utils.nix
+++ b/artiq-fast/wfvm/utils.nix
@@ -63,7 +63,7 @@ rec {
       wfvm@localhost:$1 .
   '';
 
-  wfvm-run = { name, image, script, display ? false, isolateNetwork ? true, forwardedPorts ? [] }:
+  wfvm-run = { name, image, script, display ? false, isolateNetwork ? true, forwardedPorts ? [], fakeRtc ? true }:
     let
       restrict =
         if isolateNetwork
@@ -75,7 +75,7 @@ rec {
         (map ({ listenAddr, targetAddr, port }:
           ",guestfwd=tcp:${listenAddr}:${toString port}-cmd:${pkgs.socat}/bin/socat\\ -\\ tcp:${targetAddr}:${toString port}"
         ) forwardedPorts);
-      qemuParams = mkQemuFlags (pkgs.lib.optional (!display) "-display none" ++ [
+      qemuParams = mkQemuFlags (pkgs.lib.optional (!display) "-display none" ++ pkgs.lib.optional (!fakeRtc) "-rtc base=localtime" ++ [
         "-drive"
         "file=${image},index=0,media=disk,cache=unsafe"
         "-snapshot"