diff --git a/include/sudo_event.h b/include/sudo_event.h
index bb508b3a7..61ada67ce 100644
--- a/include/sudo_event.h
+++ b/include/sudo_event.h
@@ -137,8 +137,8 @@ __dso_public int sudo_ev_set_v1(struct sudo_event *ev, int fd, short events, sud
 #define sudo_ev_set(_a, _b, _c, _d, _e) sudo_ev_set_v1((_a), (_b), (_c), (_d), (_e))
 
 /* Add an event, returns 0 on success, -1 on error */
-__dso_public int sudo_ev_add_v1(struct sudo_event_base *head, struct sudo_event *ev, struct timeval *timo, bool tohead);
-__dso_public int sudo_ev_add_v2(struct sudo_event_base *head, struct sudo_event *ev, struct timespec *timo, bool tohead);
+__dso_public int sudo_ev_add_v1(struct sudo_event_base *head, struct sudo_event *ev, const struct timeval *timo, bool tohead);
+__dso_public int sudo_ev_add_v2(struct sudo_event_base *head, struct sudo_event *ev, const struct timespec *timo, bool tohead);
 #define sudo_ev_add(_a, _b, _c, _d) sudo_ev_add_v2((_a), (_b), (_c), (_d))
 
 /* Delete an event, returns 0 on success, -1 on error */
diff --git a/lib/util/event.c b/lib/util/event.c
index 0cd89ad94..29374558d 100644
--- a/lib/util/event.c
+++ b/lib/util/event.c
@@ -454,7 +454,7 @@ sudo_ev_add_signal(struct sudo_event_base *base, struct sudo_event *ev,
 
 int
 sudo_ev_add_v1(struct sudo_event_base *base, struct sudo_event *ev,
-    struct timeval *timo, bool tohead)
+    const struct timeval *timo, bool tohead)
 {
     struct timespec tsbuf, *ts = NULL;
 
@@ -468,7 +468,7 @@ sudo_ev_add_v1(struct sudo_event_base *base, struct sudo_event *ev,
 
 int
 sudo_ev_add_v2(struct sudo_event_base *base, struct sudo_event *ev,
-    struct timespec *timo, bool tohead)
+    const struct timespec *timo, bool tohead)
 {
     debug_decl(sudo_ev_add, SUDO_DEBUG_EVENT);