diff --git a/include/osmocom/core/timer.h b/include/osmocom/core/timer.h
index db2ecbf..6c2e8c5 100644
--- a/include/osmocom/core/timer.h
+++ b/include/osmocom/core/timer.h
@@ -64,9 +64,9 @@
 /**
  * internal timer list management
  */
-struct timeval *osmo_timers_nearest();
-void osmo_timers_prepare();
-int osmo_timers_update();
+struct timeval *osmo_timers_nearest(void);
+void osmo_timers_prepare(void);
+int osmo_timers_update(void);
 int osmo_timers_check(void);
 
 #endif