diff --git a/drivers/clocksource/acpi_pm.c b/drivers/clocksource/acpi_pm.c
index 40bd8c6..72a633a 100644
--- a/drivers/clocksource/acpi_pm.c
+++ b/drivers/clocksource/acpi_pm.c
@@ -18,6 +18,7 @@
 
 #include <linux/acpi_pmtmr.h>
 #include <linux/clocksource.h>
+#include <linux/timex.h>
 #include <linux/errno.h>
 #include <linux/init.h>
 #include <linux/pci.h>