diff --git a/vendors/irmin-lmdb/irmin_lmdb.ml b/vendors/irmin-lmdb/irmin_lmdb.ml
index 2e6a147e6..39a8357db 100644
--- a/vendors/irmin-lmdb/irmin_lmdb.ml
+++ b/vendors/irmin-lmdb/irmin_lmdb.ml
@@ -641,7 +641,7 @@ module Make
         let { root ; mapsize ; readonly } = config conf in
         let root = match root with None -> "irmin.ldb" | Some root -> root in
         if not (Sys.file_exists root) then Unix.mkdir root 0o755 ;
-        let flags = Lmdb.NoTLS :: if readonly then [ Lmdb.RdOnly ] else [] in
+        let flags = Lmdb.NoRdAhead :: Lmdb.NoTLS :: if readonly then [ Lmdb.RdOnly ] else [] in
         let file_flags = if readonly then 0o444 else 0o644 in
         match Lmdb.opendir ~mapsize ~flags root file_flags with
         | Error err -> Lwt.fail_with (Lmdb.string_of_error err)