diff --git a/dap-sdk/core/src/dap_common.c b/dap-sdk/core/src/dap_common.c
index 66dc2b24bef6250517c26917240d86b6303808ac..d644b1653f4e70d00e64df6a81ba7a26df14b0c1 100755
--- a/dap-sdk/core/src/dap_common.c
+++ b/dap-sdk/core/src/dap_common.c
@@ -1172,6 +1172,7 @@ void *dap_interval_timer_create(unsigned int a_msec, dap_timer_callback_t a_call
 
     dispatch_queue_t l_queue = dispatch_queue_create("tqueue", 0);
     dispatch_source_t l_timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, l_queue);
+    //todo: we should not use ^ like this, because this is clang-specific thing, but someone can use GCC on mac os
     dispatch_source_set_event_handler(l_timer, ^(void){s_bsd_callback(s_timers_count);});
     dispatch_time_t start = dispatch_time(DISPATCH_TIME_NOW, a_msec * 1000000);
     dispatch_source_set_timer(l_timer, start, a_msec * 1000000, 0);
diff --git a/modules/channel/chain/dap_stream_ch_chain.c b/modules/channel/chain/dap_stream_ch_chain.c
index e7896660424c9f87b3189b67694a9bc735dced50..2ffbd5892e77417dc2f0a6f148f9658bb9b34493 100644
--- a/modules/channel/chain/dap_stream_ch_chain.c
+++ b/modules/channel/chain/dap_stream_ch_chain.c
@@ -646,7 +646,7 @@ dap_chain_t *dap_chain_get_chain_from_group_name(dap_chain_net_id_t a_net_id, co
     }
     dap_chain_net_t *l_net = dap_chain_net_by_id(a_net_id);
     if (!l_net)
-        return false;
+        return NULL;
     dap_chain_t *l_chain = NULL;
     DL_FOREACH(l_net->pub.chains, l_chain) {
         char *l_chain_group_name = dap_chain_net_get_gdb_group_from_chain_new(l_chain);
diff --git a/modules/service/xchange/dap_chain_net_srv_xchange.c b/modules/service/xchange/dap_chain_net_srv_xchange.c
index a689548c521220803efb6a8a953a010c4727647a..e42b695dc2f4c5970049f73b2c415a8122a19746 100644
--- a/modules/service/xchange/dap_chain_net_srv_xchange.c
+++ b/modules/service/xchange/dap_chain_net_srv_xchange.c
@@ -404,7 +404,7 @@ static dap_chain_datum_tx_t *s_xchange_tx_create_exchange(dap_chain_net_srv_xcha
     dap_chain_tx_out_cond_t *l_tx_out_cond = dap_chain_datum_tx_out_cond_get(l_cond_tx, &l_prev_cond_idx);
     if (dap_chain_ledger_tx_hash_is_used_out_item(l_ledger, &a_price->tx_hash, l_prev_cond_idx)) {
         log_it(L_WARNING, "Requested conditional transaction is already used out");
-        return false;
+        return NULL;
     }
     dap_chain_datum_tx_add_in_cond_item(&l_tx, &a_price->tx_hash, l_prev_cond_idx, 0);
     // add 'out' items