diff --git a/src/fdb_kvdb.c b/src/fdb_kvdb.c
index 6c04534..4089c79 100644
--- a/src/fdb_kvdb.c
+++ b/src/fdb_kvdb.c
@@ -1531,6 +1531,8 @@ void fdb_kvdb_control(fdb_kvdb_t db, int cmd, void *arg)
 
     switch (cmd) {
     case FDB_KVDB_CTRL_SET_SEC_SIZE:
+        /* the sector size change MUST before database initialization */
+        FDB_ASSERT(db->parent.init_ok == false);
         db->parent.sec_size = *(uint32_t *)arg;
         break;
     case FDB_KVDB_CTRL_GET_SEC_SIZE:
diff --git a/src/fdb_tsdb.c b/src/fdb_tsdb.c
index 8cd5ea8..8d99678 100644
--- a/src/fdb_tsdb.c
+++ b/src/fdb_tsdb.c
@@ -675,6 +675,8 @@ void fdb_tsdb_control(fdb_tsdb_t db, int cmd, void *arg)
         *(bool *)arg = db->rollover;
         break;
     case FDB_TSDB_CTRL_SET_SEC_SIZE:
+        /* the sector size change MUST before database initialization */
+        FDB_ASSERT(db->parent.init_ok == false);
         db->parent.sec_size = *(uint32_t *)arg;
         break;
     case FDB_TSDB_CTRL_GET_SEC_SIZE: