diff --git a/arch/arm/src/lpc17xx_40xx/hardware/lpc17_40_wdt.h b/arch/arm/src/lpc17xx_40xx/hardware/lpc17_40_wdt.h
index 6c6d1b2297..1e2d2eda58 100644
--- a/arch/arm/src/lpc17xx_40xx/hardware/lpc17_40_wdt.h
+++ b/arch/arm/src/lpc17xx_40xx/hardware/lpc17_40_wdt.h
@@ -89,7 +89,7 @@
 
 /* Watchdog feed sequence register  */
 
-#define WDT_FEED_KEY_1                (0xAA)    /* Watchdog feed key 1 */
+#define WDT_FEED_KEY_1                (0xaa)    /* Watchdog feed key 1 */
 #define WDT_FEED_KEY_2                (0x55)    /* Watchdog feed key 2 */
 #define WDT_FEED_MASK                 (0xff)    /* Bits 0-7: Feed value should be 0xaa
                                                  *           followed by 0x55 */