diff --git a/include/util/time.h b/include/util/time.h
index 76ec2d7f1..5ab4cb103 100644
--- a/include/util/time.h
+++ b/include/util/time.h
@@ -23,6 +23,12 @@ int64_t timespec_to_nsec(const struct timespec *t);
  */
 void timespec_from_nsec(struct timespec *r, int64_t nsec);
 
+/**
+ * Add two timespec values `a` and `b`, and store the result in `r`.
+ */
+void timespec_add(struct timespec *r, const struct timespec *a,
+		const struct timespec *b);
+
 /**
  * Subtracts timespec `b` from timespec `a`, and stores the difference in `r`.
  */
diff --git a/util/time.c b/util/time.c
index e3a4590ad..c02e585b5 100644
--- a/util/time.c
+++ b/util/time.c
@@ -25,12 +25,24 @@ uint32_t get_current_time_msec(void) {
 	return timespec_to_msec(&now);
 }
 
-void timespec_sub(struct timespec *r, const struct timespec *a,
+void timespec_add(struct timespec *r, const struct timespec *a,
 		const struct timespec *b) {
-	r->tv_sec = a->tv_sec - b->tv_sec;
-	r->tv_nsec = a->tv_nsec - b->tv_nsec;
-	if (r->tv_nsec < 0) {
+	r->tv_sec = a->tv_sec + b->tv_sec;
+	r->tv_nsec = a->tv_nsec + b->tv_nsec;
+	if (r->tv_nsec >= NSEC_PER_SEC) {
+		r->tv_sec++;
+		r->tv_nsec -= NSEC_PER_SEC;
+	} else if (r->tv_nsec < 0) {
 		r->tv_sec--;
 		r->tv_nsec += NSEC_PER_SEC;
 	}
 }
+
+void timespec_sub(struct timespec *r, const struct timespec *a,
+		const struct timespec *b) {
+	struct timespec tmp = {
+		.tv_sec = -b->tv_sec,
+		.tv_nsec = -b->tv_nsec,
+	};
+	timespec_add(r, a, &tmp);
+}