diff --git a/lib/sqlite3_utils.ml b/lib/sqlite3_utils.ml
index 805b2cd..9e30b54 100644
--- a/lib/sqlite3_utils.ml
+++ b/lib/sqlite3_utils.ml
@@ -8,7 +8,7 @@ let db_pool =
     Task_pool.size
     (fun () ->
        db_open
-         ~mutex:`NO
+         ~mutex:`FULL
          (CCOption.get_exn_or "Docfd_lib.Params.db_path uninitialized" !Params.db_path)
     )