diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 062e718dc3..45069f54f6 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -124,6 +124,7 @@ config ARCH_CHIP_LC823450
 	select ARCH_HAVE_MULTICPU
 	select ARCH_HAVE_I2CRESET
 	select ARCH_GLOBAL_IRQDISABLE
+	select ARCH_IDLE_CUSTOM
 	---help---
 		ON Semiconductor LC823450 architectures (ARM dual Cortex-M3)
 
diff --git a/arch/arm/src/lc823450/Make.defs b/arch/arm/src/lc823450/Make.defs
index e7af3b0ea2..fa9049b6ad 100644
--- a/arch/arm/src/lc823450/Make.defs
+++ b/arch/arm/src/lc823450/Make.defs
@@ -83,13 +83,13 @@ endif
 
 CHIP_ASRCS  =
 
-CHIP_CSRCS  = lc823450_start.c lc823450_irq.c .c lc823450_timer.c
+CHIP_CSRCS  = lc823450_start.c lc823450_irq.c lc823450_timer.c
 CHIP_CSRCS += lc823450_lowputc.c lc823450_serial.c lc823450_clockconfig.c
 CHIP_CSRCS += lc823450_syscontrol.c lc823450_gpio.c
 
 # Configuration-dependent LC823450 files
 
-ifneq ($(CONFIG_ARCH_IDLE_CUSTOM),y)
+ifeq ($(CONFIG_ARCH_IDLE_CUSTOM),y)
 CHIP_CSRCS += lc823450_idle.c
 endif