diff --git a/src/class/cdc/cdc_device.c b/src/class/cdc/cdc_device.c
index 90e1924b4c..ccb15205bb 100644
--- a/src/class/cdc/cdc_device.c
+++ b/src/class/cdc/cdc_device.c
@@ -66,7 +66,14 @@ typedef struct {
 }cdcd_interface_t;
 
 // TODO multiple rhport
+
+#if CFG_TUSB_MCU == OPT_MCU_NRF5X
+// FIXME nrf52 OUT: Controller ACK data even we didn't prepare transfer
+CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_rx_buf[600];
+#else
 CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_rx_buf[64];
+#endif
+
 CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_tx_buf[64];
 
 FIFO_DEF(_rx_ff, CFG_TUD_CDC_BUFSIZE, uint8_t, true);