diff --git a/docs/swarm/credentials.md b/docs/swarm/credentials.md
index a1aaf9b7..cfee085e 100644
--- a/docs/swarm/credentials.md
+++ b/docs/swarm/credentials.md
@@ -174,6 +174,7 @@ single attempt, not for the retries: an attempt that fails ends that start, so
 the dependent starts with whatever is already on disk. When a later attempt
 lands a changed value, the homeserver, Grafana and collector readers restart
 the service that loaded it (`nix/host-modules/lib/refresh-consumer.nix`).
+When the fetch unit can't read the credential file's mtime or the service's start time, it logs `cannot compare the mtime of <path> … — leaving <unit> as it is` at `err` in its own journal, and the service keeps running on the old value until the next timer tick.
 
 ## Progressive enhancement