diff --git a/nixos/modules/services/continuous-integration/jenkins/default.nix b/nixos/modules/services/continuous-integration/jenkins/default.nix
index 7a118ac72071..9bd511ad3ae3 100644
--- a/nixos/modules/services/continuous-integration/jenkins/default.nix
+++ b/nixos/modules/services/continuous-integration/jenkins/default.nix
@@ -128,6 +128,11 @@ in {
 
       path = cfg.packages;
 
+      # Force .war (re)extraction, or else we might run stale Jenkins.
+      preStart = ''
+        rm -rf ${cfg.home}/war
+      '';
+
       script = ''
         ${pkgs.jdk}/bin/java -jar ${pkgs.jenkins} --httpPort=${toString cfg.port} ${concatStringsSep " " cfg.extraOptions}
       '';