diff --git a/drivers/tty/serial/m32r_sio.c b/drivers/tty/serial/m32r_sio.c
index bb1afa0922e1..9cd9b4eba9fc 100644
--- a/drivers/tty/serial/m32r_sio.c
+++ b/drivers/tty/serial/m32r_sio.c
@@ -368,7 +368,10 @@ static void receive_chars(struct uart_sio_port *up, int *status)
 	ignore_char:
 		*status = serial_in(up, UART_LSR);
 	} while ((*status & UART_LSR_DR) && (max_count-- > 0));
+
+	spin_unlock(&up->port.lock);
 	tty_flip_buffer_push(port);
+	spin_lock(&up->port.lock);
 }
 
 static void transmit_chars(struct uart_sio_port *up)