diff --git a/hydra/modules/sysadmin/services.scm b/hydra/modules/sysadmin/services.scm
index caf3f23..f13efeb 100644
--- a/hydra/modules/sysadmin/services.scm
+++ b/hydra/modules/sysadmin/services.scm
@@ -693,7 +693,12 @@ to a selected directory.")
                             (authorized-keys authorized-keys)
                             (motd %default-motd)
                             (nar-ttl (* 180 24 3600))
-                            (cache-bypass-threshold (* 100 (expt 2 20))) ;100 MiB
+
+                            ;; XXX: Set a threshold larger than the Guix
+                            ;; source tree, to please system tests:
+                            ;; <https://issues.guix.gnu.org/54447#12>.
+                            (cache-bypass-threshold (* 150 MiB))
+
                             (publish-workers 6))
   "Return the list of services for the build farm frontend."
   (cons* (service mcron-service-type