diff --git a/src/l2cap_signaling.c b/src/l2cap_signaling.c
index 9b1c098ba..445c78d05 100644
--- a/src/l2cap_signaling.c
+++ b/src/l2cap_signaling.c
@@ -77,6 +77,9 @@ static uint16_t l2cap_create_signaling_internal(uint8_t * acl_buffer, hci_con_ha
             "22222", // 0x15 le credit based connection respone: dest cid, mtu, mps, initial credits, result
             "22",    // 0x16 le flow control credit: source cid, credits
 #endif
+#ifdef UNIT_TEST
+            "M",     // invalid format for unit testing
+#endif           
     };
     static const unsigned int num_l2cap_commands = sizeof(l2cap_signaling_commands_format) / sizeof(const char *);
 
diff --git a/src/l2cap_signaling.h b/src/l2cap_signaling.h
index 88c706284..cf917f75d 100644
--- a/src/l2cap_signaling.h
+++ b/src/l2cap_signaling.h
@@ -70,6 +70,9 @@ typedef enum {
     LE_CREDIT_BASED_CONNECTION_REQUEST,
     LE_CREDIT_BASED_CONNECTION_RESPONSE,
     LE_FLOW_CONTROL_CREDIT,
+#ifdef UNIT_TEST
+    COMMAND_WITH_INVALID_FORMAT,
+#endif     
     COMMAND_REJECT_LE = 0x1F  // internal to BTstack
 } L2CAP_SIGNALING_COMMANDS;