diff --git a/src/main/ezusb-iidx-emu/msg.c b/src/main/ezusb-iidx-emu/msg.c
index c7dafcb..c651042 100644
--- a/src/main/ezusb-iidx-emu/msg.c
+++ b/src/main/ezusb-iidx-emu/msg.c
@@ -160,6 +160,10 @@ static HRESULT ezusb_iidx_emu_msg_interrupt_read(struct iobuf *read)
     otherwise the game's fpga check will fail */
     msg_resp->fpga2_check_flag_unkn = 2;
 
+#ifdef EZUSB_IIDX_EMU_D01_BOARD
+    msg_resp->inverted_pad &= ~(1 << 4);
+#endif
+
     read->pos = sizeof(*msg_resp);
 
     return S_OK;
diff --git a/src/main/ezusb-iidx/msg.h b/src/main/ezusb-iidx/msg.h
index 718f149..5f81f8d 100644
--- a/src/main/ezusb-iidx/msg.h
+++ b/src/main/ezusb-iidx/msg.h
@@ -59,7 +59,9 @@ struct ezusb_iidx_msg_interrupt_read_packet {
       1: Not used
       2: Not used
       3: Not used
-      4: Not used
+      4: C02/D01 board identifier, 1 = C02, 0 = D01 (on active low). This defines how the game has
+         to flash the FPGA board since D01 needs a different firmware (see result of FPGA CHECK on
+         game bootup)
       5: Not used
       6: usb mute?
       7: Not used