diff --git a/guix-data-service/jobs/load-new-guix-revision.scm b/guix-data-service/jobs/load-new-guix-revision.scm
index ddd5a6b..dfa41ec 100644
--- a/guix-data-service/jobs/load-new-guix-revision.scm
+++ b/guix-data-service/jobs/load-new-guix-revision.scm
@@ -1770,6 +1770,7 @@ SELECT 1 FROM derivation_source_file_nars WHERE derivation_source_file_id = $1"
            (unless (valid-path? inferior-store guix-derivation)
              (simple-format #t "warning: attempting to substitute guix derivation (~A)\n"
                             guix-derivation)
+             ;; Wait until the derivations are in the database
              (fibers-force guix-revision-id-promise)
              (ensure-path inferior-store guix-derivation))
            (simple-format #t "warning: building (~A)\n"