diff --git a/libraries/libmdb/mdb.c b/libraries/libmdb/mdb.c
index 6f279e3..117a891 100644
--- a/libraries/libmdb/mdb.c
+++ b/libraries/libmdb/mdb.c
@@ -3695,7 +3695,8 @@ top:
 					offset = NODESIZE + sizeof(indx_t) + data->mv_size;
 				}
 				offset += offset & 1;
-				if (NODEDSZ(leaf) + offset >= mc->mc_txn->mt_env->me_psize / MDB_MINKEYS) {
+				if (NODESIZE + NODEKSZ(leaf) + NODEDSZ(leaf) + offset >=
+					(mc->mc_txn->mt_env->me_psize - PAGEHDRSZ) / MDB_MINKEYS) {
 					/* yes, convert it */
 					dummy.md_flags = 0;
 					if (mc->mc_db->md_flags & MDB_DUPFIXED) {