diff --git a/artiq-fast/windows/manual-test-run.nix b/artiq-fast/windows/manual-test-run.nix
index fc90cc6..a969d8a 100644
--- a/artiq-fast/windows/manual-test-run.nix
+++ b/artiq-fast/windows/manual-test-run.nix
@@ -2,10 +2,9 @@
 
 { pkgs ? import <nixpkgs> {}
 , artiqpkgs ? import ../. { inherit pkgs; }
-, diskImage ? "/opt/windows/c.img"
+, diskImage ? (import ./build.nix { inherit pkgs; })
 , qemuMem ? "2G"
 , testTimeout ? 180
-,
 }:
 
 with pkgs;
diff --git a/artiq-fast/windows/qemu.nix b/artiq-fast/windows/qemu.nix
index fc26017..26191f0 100644
--- a/artiq-fast/windows/qemu.nix
+++ b/artiq-fast/windows/qemu.nix
@@ -1,5 +1,4 @@
 { pkgs
-, diskImage
 , qemuMem
 , sshUser ? "user"
 , sshPassword ? "user"
diff --git a/artiq-fast/windows/run-test.nix b/artiq-fast/windows/run-test.nix
index 46932e1..a501b5a 100644
--- a/artiq-fast/windows/run-test.nix
+++ b/artiq-fast/windows/run-test.nix
@@ -1,7 +1,7 @@
 { pkgs
 , sipycoPkg
 , artiqPkg
-, diskImage ? "/opt/windows/c.img"
+, diskImage ? (import ./build.nix { inherit pkgs; })
 , qemuMem ? "2G"
 , testTimeout ? 600
 , testCommand ? "python -m unittest discover -v sipyco.test && python -m unittest discover -v artiq.test"
@@ -14,7 +14,6 @@ let
   escape = builtins.replaceStrings [ "\\" ] [ "\\\\" ];
   qemu = import ./qemu.nix {
     inherit pkgs qemuMem;
-    diskImage = "c.img";
   };
   # Double-escape because we produce a script from a shell heredoc
   ssh = cmd: qemu.ssh (escape cmd);
@@ -34,7 +33,9 @@ in
 
 stdenv.mkDerivation {
   name = "windows-test-runner";
-  src = ./.;
+
+  # Dummy sources
+  src = pkgs.runCommandNoCC "" {} "touch $out";
 
   propagatedBuildInputs = qemu.inputs;
   dontBuild = true;
@@ -44,16 +45,14 @@ stdenv.mkDerivation {
     #!/usr/bin/env bash
     set -e -m
 
-    # +1 day from last modification of the disk image
-    CLOCK=$(date -Is -d @$(expr $(stat -c %Y ${diskImage}) + 86400))
+    cp ${diskImage} c.img
+
     ${qemu.runQemu true forwardedPorts [
     "-boot"
     "order=c"
     "-snapshot"
     "-drive"
-    "file=${diskImage},index=0,media=disk,cache=unsafe"
-    "-rtc"
-    "base=\\$CLOCK"
+    "file=c.img,index=0,media=disk,cache=unsafe"
     "-display"
     "none"
   ]} &