diff --git a/include/villas/timing.h b/include/villas/timing.h
index de25e3d9c..b04dfdab4 100644
--- a/include/villas/timing.h
+++ b/include/villas/timing.h
@@ -47,22 +47,22 @@ uint64_t timerfd_wait(int fd);
  * @retval 0 An error occured. Maybe the timer was stopped.
  * @retval >0 The nummer of runs this timer already fired.
  */
-uint64_t timerfd_wait_until(int fd, struct timespec *until);
+uint64_t timerfd_wait_until(int fd, const struct timespec *until);
 
 /** Get delta between two timespec structs */
-struct timespec time_diff(struct timespec *start, struct timespec *end);
+struct timespec time_diff(const struct timespec *start, const struct timespec *end);
 
 /** Get sum of two timespec structs */
-struct timespec time_add(struct timespec *start, struct timespec *end);
+struct timespec time_add(const struct timespec *start, const struct timespec *end);
 
 /** Return current time as a struct timespec. */
 struct timespec time_now();
 
 /** Return the diffrence off two timestamps as double value in seconds. */
-double time_delta(struct timespec *start, struct timespec *end);
+double time_delta(const struct timespec *start, const struct timespec *end);
 
 /** Convert timespec to double value representing seconds */
-double time_to_double(struct timespec *ts);
+double time_to_double(const struct timespec *ts);
 
 /** Convert double containing seconds after 1970 to timespec. */
 struct timespec time_from_double(double secs);
\ No newline at end of file
diff --git a/lib/timing.c b/lib/timing.c
index 9f34bffb2..c2cb1e1ac 100644
--- a/lib/timing.c
+++ b/lib/timing.c
@@ -54,7 +54,7 @@ uint64_t timerfd_wait(int fd)
 	return read(fd, &runs, sizeof(runs)) < 0 ? 0 : runs;
 }
 
-uint64_t timerfd_wait_until(int fd, struct timespec *until)
+uint64_t timerfd_wait_until(int fd, const struct timespec *until)
 {
 	int ret;
 	struct itimerspec its = {
@@ -78,7 +78,7 @@ struct timespec time_now()
 	return ts;
 }
 
-struct timespec time_add(struct timespec *start, struct timespec *end)
+struct timespec time_add(const struct timespec *start, const struct timespec *end)
 {
 	struct timespec sum = {
 		.tv_sec  = end->tv_sec  + start->tv_sec,
@@ -93,7 +93,7 @@ struct timespec time_add(struct timespec *start, struct timespec *end)
 	return sum;
 }
 
-struct timespec time_diff(struct timespec *start, struct timespec *end)
+struct timespec time_diff(const struct timespec *start, const struct timespec *end)
 {
 	struct timespec diff = {
 		.tv_sec  = end->tv_sec  - start->tv_sec,
@@ -118,12 +118,12 @@ struct timespec time_from_double(double secs)
 	return ts;
 }
 
-double time_to_double(struct timespec *ts)
+double time_to_double(const struct timespec *ts)
 {
 	return ts->tv_sec + ts->tv_nsec * 1e-9;
 }
 
-double time_delta(struct timespec *start, struct timespec *end)
+double time_delta(const struct timespec *start, const struct timespec *end)
 {
 	struct timespec diff = time_diff(start, end);