diff --git a/guix-data-service/data-deletion.scm b/guix-data-service/data-deletion.scm
index e4762c9..6794bea 100644
--- a/guix-data-service/data-deletion.scm
+++ b/guix-data-service/data-deletion.scm
@@ -206,6 +206,10 @@ WHERE id IN (
   (with-postgresql-transaction
    conn
    (lambda (conn)
+     (obtain-advisory-transaction-lock
+      conn
+      'delete-revisions-from-branch)
+
      (delete-from-git-commits conn)
      (delete-jobs conn)
 
@@ -538,6 +542,10 @@ WHERE NOT EXISTS (
                          (with-postgresql-transaction
                           conn
                           (lambda (conn)
+                            (obtain-advisory-transaction-lock
+                             conn
+                             'delete-unreferenced-derivations)
+
                             (exec-query
                              conn
                              "