diff --git a/CHANGES b/CHANGES
index bc9e223f0c..ebc5c5d24b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,6 @@
+3379.	[bug]		isc_interval_zero and isc_time_epoch should be
+			"const (type)* const". [RT #31069]
+
 3378.	[bug]		Handle missing 'managed-keys-directory' better.
 			[RT #30625]
 
diff --git a/lib/isc/include/isc/timer.h b/lib/isc/include/isc/timer.h
index fa9abb16aa..79c4fe5ed1 100644
--- a/lib/isc/include/isc/timer.h
+++ b/lib/isc/include/isc/timer.h
@@ -108,8 +108,8 @@ typedef struct {
 	void		(*destroy)(isc_timermgr_t **managerp);
 	isc_result_t	(*timercreate)(isc_timermgr_t *manager,
 				       isc_timertype_t type,
-				       isc_time_t *expires,
-				       isc_interval_t *interval,
+				       const isc_time_t *expires,
+				       const isc_interval_t *interval,
 				       isc_task_t *task,
 				       isc_taskaction_t action,
 				       const void *arg,
@@ -120,7 +120,8 @@ typedef struct {
 	void		(*attach)(isc_timer_t *timer, isc_timer_t **timerp);
 	void		(*detach)(isc_timer_t **timerp);
 	isc_result_t	(*reset)(isc_timer_t *timer, isc_timertype_t type,
-				 isc_time_t *expires, isc_interval_t *interval,
+				 const isc_time_t *expires,
+				 const isc_interval_t *interval,
 				 isc_boolean_t purge);
 	isc_result_t	(*touch)(isc_timer_t *timer);
 } isc_timermethods_t;
@@ -168,8 +169,8 @@ struct isc_timer {
 isc_result_t
 isc_timer_create(isc_timermgr_t *manager,
 		 isc_timertype_t type,
-		 isc_time_t *expires,
-		 isc_interval_t *interval,
+		 const isc_time_t *expires,
+		 const isc_interval_t *interval,
 		 isc_task_t *task,
 		 isc_taskaction_t action,
 		 const void *arg,
@@ -232,8 +233,8 @@ isc_timer_create(isc_timermgr_t *manager,
 isc_result_t
 isc_timer_reset(isc_timer_t *timer,
 		isc_timertype_t type,
-		isc_time_t *expires,
-		isc_interval_t *interval,
+		const isc_time_t *expires,
+		const isc_interval_t *interval,
 		isc_boolean_t purge);
 /*%<
  * Change the timer's type, expires, and interval values to the given
diff --git a/lib/isc/timer.c b/lib/isc/timer.c
index 0da251f4c3..0c80c1f980 100644
--- a/lib/isc/timer.c
+++ b/lib/isc/timer.c
@@ -130,12 +130,12 @@ struct isc__timermgr {
 
 ISC_TIMERFUNC_SCOPE isc_result_t
 isc__timer_create(isc_timermgr_t *manager, isc_timertype_t type,
-		  isc_time_t *expires, isc_interval_t *interval,
+		  const isc_time_t *expires, const isc_interval_t *interval,
 		  isc_task_t *task, isc_taskaction_t action, const void *arg,
 		  isc_timer_t **timerp);
 ISC_TIMERFUNC_SCOPE isc_result_t
 isc__timer_reset(isc_timer_t *timer, isc_timertype_t type,
-		 isc_time_t *expires, isc_interval_t *interval,
+		 const  isc_time_t *expires, const isc_interval_t *interval,
 		 isc_boolean_t purge);
 ISC_TIMERFUNC_SCOPE isc_timertype_t
 isc__timer_gettype(isc_timer_t *timer);
@@ -392,7 +392,7 @@ destroy(isc__timer_t *timer) {
 
 ISC_TIMERFUNC_SCOPE isc_result_t
 isc__timer_create(isc_timermgr_t *manager0, isc_timertype_t type,
-		  isc_time_t *expires, isc_interval_t *interval,
+		  const isc_time_t *expires, const isc_interval_t *interval,
 		  isc_task_t *task, isc_taskaction_t action, const void *arg,
 		  isc_timer_t **timerp)
 {
@@ -514,7 +514,7 @@ isc__timer_create(isc_timermgr_t *manager0, isc_timertype_t type,
 
 ISC_TIMERFUNC_SCOPE isc_result_t
 isc__timer_reset(isc_timer_t *timer0, isc_timertype_t type,
-		 isc_time_t *expires, isc_interval_t *interval,
+		 const isc_time_t *expires, const isc_interval_t *interval,
 		 isc_boolean_t purge)
 {
 	isc__timer_t *timer = (isc__timer_t *)timer0;
diff --git a/lib/isc/timer_api.c b/lib/isc/timer_api.c
index 97e62b3f0e..c9d91c33aa 100644
--- a/lib/isc/timer_api.c
+++ b/lib/isc/timer_api.c
@@ -96,7 +96,7 @@ isc_timermgr_destroy(isc_timermgr_t **managerp) {
 
 isc_result_t
 isc_timer_create(isc_timermgr_t *manager, isc_timertype_t type,
-		 isc_time_t *expires, isc_interval_t *interval,
+		 const isc_time_t *expires, const isc_interval_t *interval,
 		 isc_task_t *task, isc_taskaction_t action, const void *arg,
 		 isc_timer_t **timerp)
 {
@@ -128,7 +128,7 @@ isc_timer_detach(isc_timer_t **timerp) {
 
 isc_result_t
 isc_timer_reset(isc_timer_t *timer, isc_timertype_t type,
-		isc_time_t *expires, isc_interval_t *interval,
+		const isc_time_t *expires, const isc_interval_t *interval,
 		isc_boolean_t purge)
 {
 	REQUIRE(ISCAPI_TIMER_VALID(timer));
diff --git a/lib/isc/unix/include/isc/time.h b/lib/isc/unix/include/isc/time.h
index dc1cef9ad3..9090929b15 100644
--- a/lib/isc/unix/include/isc/time.h
+++ b/lib/isc/unix/include/isc/time.h
@@ -41,7 +41,7 @@ struct isc_interval {
 	unsigned int nanoseconds;
 };
 
-extern isc_interval_t *isc_interval_zero;
+extern const isc_interval_t * const isc_interval_zero;
 
 ISC_LANG_BEGINDECLS
 
@@ -85,7 +85,7 @@ struct isc_time {
 	unsigned int	nanoseconds;
 };
 
-extern isc_time_t *isc_time_epoch;
+extern const isc_time_t * const isc_time_epoch;
 
 void
 isc_time_set(isc_time_t *t, unsigned int seconds, unsigned int nanoseconds);
diff --git a/lib/isc/unix/time.c b/lib/isc/unix/time.c
index ac23ae0928..e820afb1ea 100644
--- a/lib/isc/unix/time.c
+++ b/lib/isc/unix/time.c
@@ -54,8 +54,8 @@
  *** Intervals
  ***/
 
-static isc_interval_t zero_interval = { 0, 0 };
-isc_interval_t *isc_interval_zero = &zero_interval;
+static const isc_interval_t zero_interval = { 0, 0 };
+const isc_interval_t * const isc_interval_zero = &zero_interval;
 
 #if ISC_FIX_TV_USEC
 static inline void
@@ -110,8 +110,8 @@ isc_interval_iszero(const isc_interval_t *i) {
  *** Absolute Times
  ***/
 
-static isc_time_t epoch = { 0, 0 };
-isc_time_t *isc_time_epoch = &epoch;
+static const isc_time_t epoch = { 0, 0 };
+const isc_time_t * const isc_time_epoch = &epoch;
 
 void
 isc_time_set(isc_time_t *t, unsigned int seconds, unsigned int nanoseconds) {
diff --git a/lib/isc/win32/include/isc/time.h b/lib/isc/win32/include/isc/time.h
index 8ffb24b114..16be769e7e 100644
--- a/lib/isc/win32/include/isc/time.h
+++ b/lib/isc/win32/include/isc/time.h
@@ -39,7 +39,7 @@ struct isc_interval {
 	isc_int64_t interval;
 };
 
-LIBISC_EXTERNAL_DATA extern isc_interval_t *isc_interval_zero;
+LIBISC_EXTERNAL_DATA extern const isc_interval_t * const isc_interval_zero;
 
 ISC_LANG_BEGINDECLS
 
@@ -82,7 +82,7 @@ struct isc_time {
 	FILETIME absolute;
 };
 
-LIBISC_EXTERNAL_DATA extern isc_time_t *isc_time_epoch;
+LIBISC_EXTERNAL_DATA extern const isc_time_t * const isc_time_epoch;
 
 void
 isc_time_set(isc_time_t *t, unsigned int seconds, unsigned int nanoseconds);
diff --git a/lib/isc/win32/time.c b/lib/isc/win32/time.c
index aafd70b124..7ffd0de053 100644
--- a/lib/isc/win32/time.c
+++ b/lib/isc/win32/time.c
@@ -47,15 +47,15 @@
  *** Absolute Times
  ***/
 
-static isc_time_t epoch = { { 0, 0 } };
-LIBISC_EXTERNAL_DATA isc_time_t *isc_time_epoch = &epoch;
+static const isc_time_t epoch = { { 0, 0 } };
+LIBISC_EXTERNAL_DATA const isc_time_t * const isc_time_epoch = &epoch;
 
 /***
  *** Intervals
  ***/
 
-static isc_interval_t zero_interval = { 0 };
-LIBISC_EXTERNAL_DATA isc_interval_t *isc_interval_zero = &zero_interval;
+static const isc_interval_t zero_interval = { 0 };
+LIBISC_EXTERNAL_DATA const isc_interval_t * const isc_interval_zero = &zero_interval;
 
 void
 isc_interval_set(isc_interval_t *i, unsigned int seconds,