diff --git a/guix-data-service/utils.scm b/guix-data-service/utils.scm
index 393db95..48f9c88 100644
--- a/guix-data-service/utils.scm
+++ b/guix-data-service/utils.scm
@@ -60,6 +60,7 @@
 
             fibers-delay
             fibers-force
+            fibers-promise-reset
 
             fibers-batch-for-each
             fibers-for-each
@@ -797,6 +798,10 @@ If already in the worker thread, call PROC immediately."
                 (raise-exception res)
                 (apply values res))))))
 
+(define (fibers-promise-reset fp)
+  (atomic-box-set! (fibers-promise-values-box fp)
+                   #f))
+
 (define (fibers-batch-for-each proc batch-size . lists)
   ;; Like split-at, but don't care about the order of the resulting lists, and
   ;; don't error if the list is shorter than i elements