diff --git a/libraries/mbed/targets/cmsis/TARGET_NXP/TARGET_LPC11XX/system_LPC11xx.c b/libraries/mbed/targets/cmsis/TARGET_NXP/TARGET_LPC11XX/system_LPC11xx.c
index b1fb04dd54..f321255d9c 100644
--- a/libraries/mbed/targets/cmsis/TARGET_NXP/TARGET_LPC11XX/system_LPC11xx.c
+++ b/libraries/mbed/targets/cmsis/TARGET_NXP/TARGET_LPC11XX/system_LPC11xx.c
@@ -108,8 +108,8 @@
 #define SYSOSCCTRL_Val        0x00000000              // Reset: 0x000
 #define WDTOSCCTRL_Val        0x00000000              // Reset: 0x000
 #define SYSPLLCTRL_Val        0x00000023              // Reset: 0x000
-#define SYSPLLCLKSEL_Val      0x00000001              // Reset: 0x000
-#define MAINCLKSEL_Val        0x00000000              // Reset: 0x000
+#define SYSPLLCLKSEL_Val      0x00000000              // Reset: 0x000	// Define as using IRC
+#define MAINCLKSEL_Val        0x00000003              // Reset: 0x000	// Define as using System PLL clock out
 #define SYSAHBCLKDIV_Val      0x00000001              // Reset: 0x001
 
 /*