diff --git a/include/osmocom/core/timer.h b/include/osmocom/core/timer.h
index 6ffc3b1..61d20e2 100644
--- a/include/osmocom/core/timer.h
+++ b/include/osmocom/core/timer.h
@@ -75,7 +75,7 @@
 
 void osmo_timer_del(struct osmo_timer_list *timer);
 
-int osmo_timer_pending(struct osmo_timer_list *timer);
+int osmo_timer_pending(const struct osmo_timer_list *timer);
 
 int osmo_timer_remaining(const struct osmo_timer_list *timer,
 			 const struct timeval *now,