diff --git a/arch/arm/src/nuc1xx/nuc_timerisr.c b/arch/arm/src/nuc1xx/nuc_timerisr.c
index b6eff265c60..d80f14d0822 100644
--- a/arch/arm/src/nuc1xx/nuc_timerisr.c
+++ b/arch/arm/src/nuc1xx/nuc_timerisr.c
@@ -101,7 +101,7 @@
  *
  ****************************************************************************/
 
-#ifdef CONFIG_NUC_SYSTICK_CORECLK
+#ifndef CONFIG_NUC_SYSTICK_CORECLK
 static inline void nuc_unlock(void)
 {
   putreg32(0x59, NUC_GCR_REGWRPROT);
@@ -124,7 +124,7 @@ static inline void nuc_unlock(void)
  *
  ****************************************************************************/
 
-#ifdef CONFIG_NUC_SYSTICK_CORECLK
+#ifndef CONFIG_NUC_SYSTICK_CORECLK
 static inline void nuc_lock(void)
 {
   putreg32(0, NUC_GCR_REGWRPROT);