diff --git a/common_arm/usb_cdc.c b/common_arm/usb_cdc.c
index c37a9934e..cc3534dc1 100644
--- a/common_arm/usb_cdc.c
+++ b/common_arm/usb_cdc.c
@@ -716,7 +716,7 @@ uint32_t usb_read(uint8_t *data, size_t len) {
 
 static uint8_t usb_read_ng_buffer[64] = {0};
 static uint8_t usb_read_ng_bufoffset = 0;
-static uint16_t usb_read_ng_buflen = 0;
+static size_t usb_read_ng_buflen = 0;
 
 bool usb_read_ng_has_buffered_data(void) {
     return usb_read_ng_buflen > 0;