diff --git a/cmd/restic/cmd_check.go b/cmd/restic/cmd_check.go
index b4e922445..33b5f3725 100644
--- a/cmd/restic/cmd_check.go
+++ b/cmd/restic/cmd_check.go
@@ -50,7 +50,7 @@ func init() {
 
 	f := cmdCheck.Flags()
 	f.BoolVar(&checkOptions.ReadData, "read-data", false, "read all data blobs")
-	f.StringVar(&checkOptions.ReadDataSubset, "read-data-subset", "", "read subset of data packs")
+	f.StringVar(&checkOptions.ReadDataSubset, "read-data-subset", "", "read subset n of m data packs (format: `n/m`)")
 	f.BoolVar(&checkOptions.CheckUnused, "check-unused", false, "find unused blobs")
 	f.BoolVar(&checkOptions.WithCache, "with-cache", false, "use the cache")
 }