diff --git a/src/btstack_crypto.c b/src/btstack_crypto.c
index 7d2da4160..85eba6685 100644
--- a/src/btstack_crypto.c
+++ b/src/btstack_crypto.c
@@ -107,7 +107,7 @@ typedef enum {
 
 static void btstack_crypto_run(void);
 
-const static uint8_t zero[16] = { 0 };
+static const uint8_t zero[16] = { 0 };
 
 static uint8_t btstack_crypto_initialized;
 static btstack_linked_list_t btstack_crypto_operations;
diff --git a/src/classic/btstack_link_key_db_static.c b/src/classic/btstack_link_key_db_static.c
index c7afc2068..fd72d3035 100644
--- a/src/classic/btstack_link_key_db_static.c
+++ b/src/classic/btstack_link_key_db_static.c
@@ -123,6 +123,7 @@ static int link_key_db_get_link_key(bd_addr_t bd_addr, link_key_t link_key, link
 }
 
 static void link_key_db_delete_link_key(bd_addr_t bd_addr){
+    (void) bd_addr;
 }
 
 
@@ -132,6 +133,7 @@ static void link_key_db_put_link_key(bd_addr_t bd_addr, link_key_t link_key, lin
 }
 
 static void link_key_db_set_local_bd_addr(bd_addr_t bd_addr){
+    (void) bd_addr;
 }
 
 static int link_key_db_tlv_iterator_init(btstack_link_key_iterator_t * it){
@@ -142,7 +144,7 @@ static int link_key_db_tlv_iterator_init(btstack_link_key_iterator_t * it){
 static int  link_key_db_tlv_iterator_get_next(btstack_link_key_iterator_t * it, bd_addr_t bd_addr, link_key_t link_key, link_key_type_t * link_key_type){
     uintptr_t i = (uintptr_t) it->context;
 
-    int num_entries = sizeof(link_key_db) / sizeof(link_key_entry_t);
+    unsigned int num_entries = sizeof(link_key_db) / sizeof(link_key_entry_t);
     if (i >= num_entries) return 0;
 
     // fetch values
diff --git a/src/hci_transport_em9304_spi.c b/src/hci_transport_em9304_spi.c
index fc923d164..aaea368c9 100644
--- a/src/hci_transport_em9304_spi.c
+++ b/src/hci_transport_em9304_spi.c
@@ -482,6 +482,7 @@ static void hci_transport_em9304_spi_block_sent(void){
 }
 
 static int hci_transport_em9304_spi_can_send_now(uint8_t packet_type){
+    UNUSED(packet_type);
     return tx_state == TX_IDLE;
 }
 
@@ -499,6 +500,7 @@ static int hci_transport_em9304_spi_send_packet(uint8_t packet_type, uint8_t * p
 }
 
 static void hci_transport_em9304_spi_init(const void * transport_config){
+    UNUSED(transport_config);
 }
 
 static int hci_transport_em9304_spi_open(void){
@@ -524,6 +526,9 @@ static void hci_transport_em9304_spi_register_packet_handler(void (*handler)(uin
 }
 
 static void dummy_handler(uint8_t packet_type, uint8_t *packet, uint16_t size){
+    UNUSED(packet_type);
+    UNUSED(packet);
+    UNUSED(size);
 }
 
 // --- end of eHCILL implementation ---------
diff --git a/src/hci_transport_h4.c b/src/hci_transport_h4.c
index 1253ff644..2b3e32a4b 100644
--- a/src/hci_transport_h4.c
+++ b/src/hci_transport_h4.c
@@ -343,6 +343,7 @@ static void hci_transport_h4_block_sent(void){
 }
 
 static int hci_transport_h4_can_send_now(uint8_t packet_type){
+    UNUSED(packet_type);
     return tx_state == TX_IDLE;
 }
 
@@ -442,6 +443,9 @@ static void hci_transport_h4_register_packet_handler(void (*handler)(uint8_t pac
 }
 
 static void dummy_handler(uint8_t packet_type, uint8_t *packet, uint16_t size){
+    UNUSED(packet_type);
+    UNUSED(packet);
+    UNUSED(size);
 }
 
 //
diff --git a/src/hci_transport_h5.c b/src/hci_transport_h5.c
index 221dde9ff..9af6d54b2 100644
--- a/src/hci_transport_h5.c
+++ b/src/hci_transport_h5.c
@@ -197,6 +197,7 @@ static uint16_t crc16_calc_for_slip_frame(const uint8_t * header, const uint8_t
 
 // -----------------------------
 static void hci_transport_inactivity_timeout_handler(btstack_timer_source_t * ts){
+    UNUSED(ts);
     log_info("inactivity timeout. link state %d, peer asleep %u, actions 0x%02x, outgoing packet %u",
         link_state, link_peer_asleep, hci_transport_link_actions, hci_transport_link_have_outgoing_packet());
     if (hci_transport_link_have_outgoing_packet()) return;
@@ -440,7 +441,8 @@ static void hci_transport_link_set_timer(uint16_t timeout_ms){
     btstack_run_loop_add_timer(&link_timer);
 }
 
-static void hci_transport_link_timeout_handler(btstack_timer_source_t * timer){
+static void hci_transport_link_timeout_handler(btstack_timer_source_t * ts){
+    UNUSED(ts);
     switch (link_state){
         case LINK_UNINITIALIZED:
             hci_transport_link_actions |= HCI_TRANSPORT_LINK_SEND_SYNC;