diff --git a/mod/silverbox/box.c b/mod/silverbox/box.c
index 1b38fef4c2a7dc53f87511b7e97d4a820ee240e9..47a209f0d2c1514a73758c78f6d07a1cd42c79c7 100644
--- a/mod/silverbox/box.c
+++ b/mod/silverbox/box.c
@@ -1815,6 +1815,7 @@ mod_init(void)
 			palloc(eter_pool, sizeof(cfg.namespace[n]->index[0][0]));
 		cfg.namespace[n]->index[1] = NULL;
 		cfg.namespace[n]->index[0]->type = "HASH";
+		cfg.namespace[n]->index[0]->unique = 1;
 		cfg.namespace[n]->index[0]->key_field =
 			palloc(eter_pool, 2 * sizeof(cfg.namespace[n]->index[0]->key_field[0]));
 		cfg.namespace[n]->index[0]->key_field[0] =