diff --git a/src/fdb_tsdb.c b/src/fdb_tsdb.c
index 5f4f9fb..8506599 100644
--- a/src/fdb_tsdb.c
+++ b/src/fdb_tsdb.c
@@ -458,6 +458,7 @@ void fdb_tsl_iter(fdb_tsdb_t db, fdb_tsl_cb cb, void *arg)
     }
 
     sec_addr = db->oldest_addr;
+    db_lock(db);
     /* search all sectors */
     do {
         traversed_len += db_sec_size(db);
@@ -476,11 +477,13 @@ void fdb_tsl_iter(fdb_tsdb_t db, fdb_tsl_cb cb, void *arg)
                 read_tsl(db, &tsl);
                 /* iterator is interrupted when callback return true */
                 if (cb(&tsl, arg)) {
+                    db_unlock(db);
                     return;
                 }
             } while ((tsl.addr.index = get_next_tsl_addr(&sector, &tsl)) != FAILED_ADDR);
         }
     } while ((sec_addr = get_next_sector_addr(db, &sector, traversed_len)) != FAILED_ADDR);
+    db_unlock(db);
 }
 
 /**
@@ -505,6 +508,7 @@ void fdb_tsl_iter_reverse(fdb_tsdb_t db, fdb_tsl_cb cb, void *cb_arg)
     }
 
     sec_addr = db->cur_sec.addr;
+    db_lock(db);
     /* search all sectors */
     do {
         traversed_len += db_sec_size(db);
@@ -523,12 +527,15 @@ void fdb_tsl_iter_reverse(fdb_tsdb_t db, fdb_tsl_cb cb, void *cb_arg)
                 read_tsl(db, &tsl);
                 /* iterator is interrupted when callback return true */
                 if (cb(&tsl, cb_arg)) {
-                    return;
+                    goto __exit;
                 }
             } while ((tsl.addr.index = get_last_tsl_addr(&sector, &tsl)) != FAILED_ADDR);
         } else if (sector.status == FDB_SECTOR_STORE_EMPTY || sector.status == FDB_SECTOR_STORE_UNUSED)
-            return;
+            goto __exit;
     } while ((sec_addr = get_last_sector_addr(db, &sector, traversed_len)) != FAILED_ADDR);
+
+__exit:
+    db_unlock(db);
 }
 
 /*
@@ -603,6 +610,7 @@ void fdb_tsl_iter_by_time(fdb_tsdb_t db, fdb_time_t from, fdb_time_t to, fdb_tsl
     }
 
     sec_addr = start_addr;
+    db_lock(db);
     /* search all sectors */
     do {
         traversed_len += db_sec_size(db);
@@ -633,18 +641,21 @@ void fdb_tsl_iter_by_time(fdb_tsdb_t db, fdb_time_t from, fdb_time_t to, fdb_tsl
                                 || (from > to && tsl.time <= from && tsl.time >= to)) {
                             /* iterator is interrupted when callback return true */
                             if (cb(&tsl, cb_arg)) {
-                                return;
+                                goto __exit;
                             }
                         } else {
-                            return;
+                            goto __exit;
                         }
                     }
                 } while ((tsl.addr.index = get_tsl_addr(&sector, &tsl)) != FAILED_ADDR);
             }
         } else if (sector.status == FDB_SECTOR_STORE_EMPTY) {
-            return;
+            goto __exit;
         }
     } while ((sec_addr = get_sector_addr(db, &sector, traversed_len)) != FAILED_ADDR);
+
+__exit:
+    db_unlock(db);
 }
 
 static bool query_count_cb(fdb_tsl_t tsl, void *arg)