diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index b1b385692f46..d0035946b6b9 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -80,10 +80,13 @@ module_param(nocst, uint, 0000);
 static unsigned int latency_factor __read_mostly = 2;
 module_param(latency_factor, uint, 0644);
 
+#ifdef CONFIG_ACPI_PROCFS
 static u64 us_to_pm_timer_ticks(s64 t)
 {
 	return div64_u64(t * PM_TIMER_FREQUENCY, 1000000);
 }
+#endif
+
 /*
  * IBM ThinkPad R40e crashes mysteriously when going into C2 or C3.
  * For now disable this. Probably a bug somewhere else.