diff --git a/ports/stm32/usbd_cdc_interface.c b/ports/stm32/usbd_cdc_interface.c
index 65f60e37c1..bdd7a4ec70 100644
--- a/ports/stm32/usbd_cdc_interface.c
+++ b/ports/stm32/usbd_cdc_interface.c
@@ -267,7 +267,7 @@ int8_t usbd_cdc_receive(usbd_cdc_state_t *cdc_in, size_t len) {
 
     // copy the incoming data into the circular buffer
     for (const uint8_t *src = cdc->rx_packet_buf, *top = cdc->rx_packet_buf + len; src < top; ++src) {
-        if (cdc->attached_to_repl && mp_interrupt_char != -1 && *src == mp_interrupt_char) {
+        if (cdc->attached_to_repl && *src == mp_interrupt_char) {
             pendsv_kbd_intr();
         } else {
             uint16_t next_put = (cdc->rx_buf_put + 1) & (USBD_CDC_RX_DATA_SIZE - 1);