diff --git a/src/hci_transport_h4.c b/src/hci_transport_h4.c
index 71d0ee9bf..4da9b10a2 100644
--- a/src/hci_transport_h4.c
+++ b/src/hci_transport_h4.c
@@ -238,6 +238,9 @@ static int    h4_process(struct data_source *ds) {
                 bytes_to_read = HCI_ACL_DATA_PKT_HDR;
                 h4_state = H4_W4_ACL_HEADER;
             } else {
+                fprintf(stderr, "h4_process: invalid packet type 0x%02x\n");
+                read_pos = 0;
+                bytes_to_read = 1;
             }
             break;
         case H4_W4_EVENT_HEADER: