diff --git a/src/timer.c b/src/timer.c
index bcd9f5b..ed5a610 100644
--- a/src/timer.c
+++ b/src/timer.c
@@ -135,7 +135,7 @@
  * This function can be used to determine whether a given timer
  * has alredy expired (returns 0) or is still pending (returns 1)
  */
-int osmo_timer_pending(struct osmo_timer_list *timer)
+int osmo_timer_pending(const struct osmo_timer_list *timer)
 {
 	return timer->active;
 }