diff --git a/include/linux/time.h b/include/linux/time.h
index 05f9517..e15206a 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -170,10 +170,13 @@
  * timespec_add_ns - Adds nanoseconds to a timespec
  * @a:		pointer to timespec to be incremented
  * @ns:		unsigned nanoseconds value to be added
+ *
+ * This must always be inlined because its used from the x86-64 vdso,
+ * which cannot call other kernel functions.
  */
-static inline void timespec_add_ns(struct timespec *a, u64 ns)
+static __always_inline void timespec_add_ns(struct timespec *a, u64 ns)
 {
-	a->tv_sec += iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
+	a->tv_sec += __iter_div_u64_rem(a->tv_nsec + ns, NSEC_PER_SEC, &ns);
 	a->tv_nsec = ns;
 }
 #endif /* __KERNEL__ */