diff --git a/firmware/src_simtrace/mode_cardemu.c b/firmware/src_simtrace/mode_cardemu.c
index ece4da8c..e51e9905 100644
--- a/firmware/src_simtrace/mode_cardemu.c
+++ b/firmware/src_simtrace/mode_cardemu.c
@@ -145,7 +145,7 @@ void usart_irq_rx(uint8_t uart)
 	if (uart == 1)
 		ci = &cardem_inst[1];
 #endif
-	csr = usart->US_CSR;
+	csr = usart->US_CSR & usart->US_IMR;
 
 	if (csr & US_CSR_RXRDY) {
         	byte = (usart->US_RHR) & 0xFF;