diff --git a/src/btstack_defines.h b/src/btstack_defines.h
index 0621f09aa..55986afe0 100644
--- a/src/btstack_defines.h
+++ b/src/btstack_defines.h
@@ -294,6 +294,13 @@
 // data: event(8)
 #define DAEMON_EVENT_HCI_PACKET_SENT                       0x6C
 
+// additional HCI events
+/**
+ * @format B
+ * @param handle
+ */
+#define HCI_EVENT_SCO_CAN_SEND_NOW                         0x6F
+
 // L2CAP EVENTS
     
 /**
diff --git a/src/hci.c b/src/hci.c
index a193e75f2..3645bcc17 100644
--- a/src/hci.c
+++ b/src/hci.c
@@ -419,13 +419,19 @@ int hci_can_send_acl_packet_now(hci_con_handle_t con_handle){
 }
 
 int hci_can_send_prepared_sco_packet_now(hci_con_handle_t con_handle){
-    if (!hci_transport_can_send_prepared_packet_now(HCI_SCO_DATA_PACKET)) return 0;
+    if (!hci_transport_can_send_prepared_packet_now(HCI_SCO_DATA_PACKET)) {
+        hci_stack->sco_waiting_for_can_send_now = 1;
+        return 0;
+    }
     if (!hci_stack->synchronous_flow_control_enabled) return 1;
     return hci_number_free_sco_slots_for_handle(con_handle) > 0;    
 }
 
 int hci_can_send_sco_packet_now(hci_con_handle_t con_handle){
-    if (hci_stack->hci_packet_buffer_reserved) return 0;
+    if (hci_stack->hci_packet_buffer_reserved) {
+        hci_stack->sco_waiting_for_can_send_now = 1;
+        return 0;
+    }
     return hci_can_send_prepared_sco_packet_now(con_handle);
 }
 
@@ -1424,7 +1430,7 @@ static void event_handler(uint8_t *packet, int size){
                         log_error("hci_number_completed_packets, more sco slots freed then sent.");
                         conn->num_sco_packets_sent = 0;
                     }
-
+                    hci_notify_sco_can_send_now(handle);
                 } else {
                     if (conn->num_acl_packets_sent >= num_packets){
                         conn->num_acl_packets_sent -= num_packets;
@@ -2900,6 +2906,23 @@ static void hci_emit_acl_packet(uint8_t * packet, uint16_t size){
     hci_stack->acl_packet_handler(HCI_ACL_DATA_PACKET, packet, size);
 }
 
+static void hci_emit_sco_can_send_now(uint16_t handle){
+    uint8_t event[4];
+    event[0] = HCI_EVENT_SCO_CAN_SEND_NOW;
+    event[1] = 2;
+    little_endian_store_16(event, 2, handle);
+    hci_dump_packet(HCI_EVENT_PACKET, 1, event, sizeof(event));
+    hci_stack->sco_packet_handler(HCI_EVENT_PACKET, handle, event, sizeof(event));
+}
+
+static void hci_notify_sco_can_send_now(uint16_t handle){
+    // notify SCO sender if waiting
+    if (hci_stack->sco_waiting_for_can_send_now){
+        hci_stack->sco_waiting_for_can_send_now = 0;
+        hci_emit_sco_can_send_now(handle);
+    }
+}
+
 void hci_emit_state(void){
     log_info("BTSTACK_EVENT_STATE %u", hci_stack->state);
     uint8_t event[3];
diff --git a/src/hci.h b/src/hci.h
index 05afbeda5..1f0b85735 100644
--- a/src/hci.h
+++ b/src/hci.h
@@ -525,6 +525,21 @@ typedef struct {
     /* link key db */
     const btstack_link_key_db_t * link_key_db;
 
+    // list of existing baseband connections
+    btstack_linked_list_t     connections;
+
+    /* callback to L2CAP layer */
+    void (*acl_packet_handler)(uint8_t packet_type, uint8_t *packet, uint16_t size);
+
+    /* callback for SCO data */
+    void (*sco_packet_handler)(uint8_t packet_type, uint8_t *packet, uint16_t size);
+
+    /* callbacks for events */
+    btstack_linked_list_t event_handlers;
+
+    // hardware error callback
+    void (*hardware_error_callback)(void);
+
     // basic configuration
     const char *       local_name;
     uint32_t           class_of_device;
@@ -534,9 +549,6 @@ typedef struct {
     uint8_t            ssp_authentication_requirement;
     uint8_t            ssp_auto_accept;
     
-    // list of existing baseband connections
-    btstack_linked_list_t     connections;
-
     // single buffer for HCI packet assembly + additional prebuffer for H4 drivers
     uint8_t   hci_packet_buffer_prefix[HCI_OUTGOING_PRE_BUFFER_SIZE];
     uint8_t   hci_packet_buffer[HCI_PACKET_BUFFER_SIZE]; // opcode (16), len(8)
@@ -553,6 +565,7 @@ typedef struct {
     uint8_t  synchronous_flow_control_enabled;
     uint8_t  le_acl_packets_total_num;
     uint16_t le_data_packets_length;
+    uint8_t  sco_waiting_for_can_send_now;
 
     /* local supported features */
     uint8_t local_supported_features[8];
@@ -572,14 +585,6 @@ typedef struct {
     // usable packet types given acl_data_packet_length and HCI_ACL_BUFFER_SIZE
     uint16_t packet_types;
     
-    /* callback to L2CAP layer */
-    void (*acl_packet_handler)(uint8_t packet_type, uint8_t *packet, uint16_t size);
-
-    /* callback for SCO data */
-    void (*sco_packet_handler)(uint8_t packet_type, uint8_t *packet, uint16_t size);
-
-    /* callbacks for events */
-    btstack_linked_list_t event_handlers;
     
     /* hci state machine */
     HCI_STATE      state;
@@ -641,9 +646,6 @@ typedef struct {
     bd_addr_t custom_bd_addr; 
     uint8_t   custom_bd_addr_set;
 
-    // hardware error callback
-    void (*hardware_error_callback)(void);
-
 } hci_stack_t;
 
 /**