diff --git a/guix-data-service/jobs/load-new-guix-revision.scm b/guix-data-service/jobs/load-new-guix-revision.scm
index 1d740a7..5034dcc 100644
--- a/guix-data-service/jobs/load-new-guix-revision.scm
+++ b/guix-data-service/jobs/load-new-guix-revision.scm
@@ -1229,7 +1229,7 @@ SELECT 1 FROM derivation_source_file_nars WHERE derivation_source_file_id = $1"
          derivation-ids
          (insert-derivations)))
 
-    (unless (null? derivations)
+    (unless (= 0 (vector-length derivations))
       (fibers-parallel
        (derivations-insert-sources postgresql-connection-pool
                                    call-with-utility-thread