diff --git a/vendors/ocaml-lmdb/src/mdb.c b/vendors/ocaml-lmdb/src/mdb.c
index a487e156f..85f5bc3fb 100644
--- a/vendors/ocaml-lmdb/src/mdb.c
+++ b/vendors/ocaml-lmdb/src/mdb.c
@@ -7620,6 +7620,7 @@ more:
 						break;
 					}
 					/* FALLTHRU: Big enough MDB_DUPFIXED sub-page */
+					__attribute__ ((fallthrough));
 				case MDB_CURRENT:
 					fp->mp_flags |= P_DIRTY;
 					COPY_PGNO(fp->mp_pgno, mp->mp_pgno);