diff --git a/src/hci.c b/src/hci.c
index b19dcda48..01075b44c 100644
--- a/src/hci.c
+++ b/src/hci.c
@@ -558,23 +558,27 @@ int hci_send_sco_packet_buffer(int size){
     }
 
     uint8_t * packet = hci_stack->hci_packet_buffer;
-    hci_con_handle_t con_handle = READ_ACL_CONNECTION_HANDLE(packet);   // same for ACL and SCO
 
-    // check for free places on Bluetooth module
-    if (!hci_can_send_prepared_sco_packet_now(con_handle)) {
-        log_error("hci_send_sco_packet_buffer called but no free ACL buffers on controller");
-        hci_release_packet_buffer();
-        return BTSTACK_ACL_BUFFERS_FULL;
-    }
+    // skip checks in loopback mode
+    if (!hci_stack->loopback_mode){
+        hci_con_handle_t con_handle = READ_ACL_CONNECTION_HANDLE(packet);   // same for ACL and SCO
 
-    // track send packet in connection struct
-    hci_connection_t *connection = hci_connection_for_handle( con_handle);
-    if (!connection) {
-        log_error("hci_send_sco_packet_buffer called but no connection for handle 0x%04x", con_handle);
-        hci_release_packet_buffer();
-        return 0;
+        // check for free places on Bluetooth module
+        if (!hci_can_send_prepared_sco_packet_now(con_handle)) {
+            log_error("hci_send_sco_packet_buffer called but no free ACL buffers on controller");
+            hci_release_packet_buffer();
+            return BTSTACK_ACL_BUFFERS_FULL;
+        }
+
+        // track send packet in connection struct
+        hci_connection_t *connection = hci_connection_for_handle( con_handle);
+        if (!connection) {
+            log_error("hci_send_sco_packet_buffer called but no connection for handle 0x%04x", con_handle);
+            hci_release_packet_buffer();
+            return 0;
+        }
+        connection->num_sco_packets_sent++;
     }
-    connection->num_sco_packets_sent++;
 
     hci_dump_packet( HCI_SCO_DATA_PACKET, 0, packet, size);
     return hci_stack->hci_transport->send_packet(HCI_SCO_DATA_PACKET, packet, size);
@@ -2610,6 +2614,10 @@ int hci_send_cmd_packet(uint8_t *packet, int size){
         }
     }
 
+    if (IS_COMMAND(packet, hci_write_loopback_mode)){
+        hci_stack->loopback_mode = packet[3];
+    }
+
 #ifdef HAVE_BLE
     if (IS_COMMAND(packet, hci_le_set_advertising_parameters)){
         hci_stack->adv_addr_type = packet[8];
diff --git a/src/hci.h b/src/hci.h
index 1b17d42c9..69b1a1276 100644
--- a/src/hci.h
+++ b/src/hci.h
@@ -131,6 +131,7 @@ extern "C" {
 #define OGF_CONTROLLER_BASEBAND   0x03
 #define OGF_INFORMATIONAL_PARAMETERS 0x04
 #define OGF_STATUS_PARAMETERS     0x05
+#define OGF_TESTING               0x06
 #define OGF_LE_CONTROLLER 0x08
 #define OGF_BTSTACK 0x3d
 #define OGF_VENDOR  0x3f
@@ -720,6 +721,8 @@ typedef struct {
     
     uint16_t   sco_voice_setting;
 
+    uint8_t   loopback_mode;
+
     // buffer for single connection decline
     uint8_t   decline_reason;
     bd_addr_t decline_addr;