diff --git a/tinyusb/class/cdc/cdc_device.c b/tinyusb/class/cdc/cdc_device.c
index 26994362b..afb140f9e 100644
--- a/tinyusb/class/cdc/cdc_device.c
+++ b/tinyusb/class/cdc/cdc_device.c
@@ -68,7 +68,7 @@ typedef struct {
 // TODO multiple rhport
 #if CFG_TUSB_MCU == OPT_MCU_NRF5X
 // FIXME nrf52 OUT bug ( Controller ACK data even we didn't prepare transfer )
-CFG_TUSB_ATTR_USBRAM CFG_TUSB_MEM_ALIGN uint8_t _tmp_rx_buf[1024];
+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