diff --git a/src/restic/repository/master_index.go b/src/restic/repository/master_index.go
index 165bf6024..8019d8781 100644
--- a/src/restic/repository/master_index.go
+++ b/src/restic/repository/master_index.go
@@ -46,9 +46,8 @@ func (mi *MasterIndex) LookupSize(id restic.ID, tpe restic.BlobType) (uint, erro
 	defer mi.idxMutex.RUnlock()
 
 	for _, idx := range mi.idx {
-		length, err := idx.LookupSize(id, tpe)
-		if err == nil {
-			return length, nil
+		if idx.Has(id, tpe) {
+			return idx.LookupSize(id, tpe)
 		}
 	}