diff --git a/bsp/sam7x/serial.c b/bsp/sam7x/serial.c
index afc61c816..5a16778bf 100644
--- a/bsp/sam7x/serial.c
+++ b/bsp/sam7x/serial.c
@@ -137,8 +137,8 @@ static rt_err_t rt_serial_init (rt_device_t dev)
 
 	RT_ASSERT(serial != RT_NULL);
 	/* must be US0 or US1 */
-	RT_ASSERT((serial->peripheral_id != AT91C_ID_US0) &&
-			  (serial->peripheral_id != AT91C_ID_US1));
+	RT_ASSERT((serial->peripheral_id == AT91C_ID_US0) ||
+			  (serial->peripheral_id == AT91C_ID_US1));
 
 	/* Enable Clock for USART */
 	AT91C_PMC_PCER = 1 << serial->peripheral_id;