diff --git a/bluetooth/1.0/default/h4_protocol.cc b/bluetooth/1.0/default/h4_protocol.cc
index 2008b00..5a89557 100644
--- a/bluetooth/1.0/default/h4_protocol.cc
+++ b/bluetooth/1.0/default/h4_protocol.cc
@@ -81,6 +81,12 @@
       }
     }
     hci_packet_type_ = static_cast<HciPacketType>(buffer[0]);
+    if (hci_packet_type_ != HCI_PACKET_TYPE_ACL_DATA &&
+        hci_packet_type_ != HCI_PACKET_TYPE_SCO_DATA &&
+        hci_packet_type_ != HCI_PACKET_TYPE_EVENT) {
+      LOG_ALWAYS_FATAL("%s: Unimplemented packet type %d", __func__,
+                       static_cast<int>(hci_packet_type_));
+    }
   } else {
     hci_packetizer_.OnDataReady(fd, hci_packet_type_);
   }