diff --git a/repo/manifest/manifest_manager.go b/repo/manifest/manifest_manager.go
index 5160c4c25..16a473d1e 100644
--- a/repo/manifest/manifest_manager.go
+++ b/repo/manifest/manifest_manager.go
@@ -23,6 +23,7 @@
 // ErrNotFound is returned when the metadata item is not found.
 var ErrNotFound = errors.New("not found")
 
+// ContentPrefix is the prefix of the content id for manifests
 const ContentPrefix = "m"
 const autoCompactionContentCount = 16