diff --git a/include/posix/time.h b/include/posix/time.h
index e0b53a5d38e..ddf51c80316 100644
--- a/include/posix/time.h
+++ b/include/posix/time.h
@@ -49,18 +49,8 @@ static inline s32_t _ts_to_ms(const struct timespec *to)
 	return (to->tv_sec * MSEC_PER_SEC) + (to->tv_nsec / NSEC_PER_MSEC);
 }
 
-/**
- * @brief Set clock time.
- *
- * See IEEE 1003.1
- */
-static inline int clock_settime(clockid_t clock_id, const struct timespec *ts)
-{
-	errno = ENOSYS;
-	return -1;
-}
-
 int clock_gettime(clockid_t clock_id, struct timespec *ts);
+int clock_settime(clockid_t clock_id, const struct timespec *ts);
 /* Timer APIs */
 int timer_create(clockid_t clockId, struct sigevent *evp, timer_t *timerid);
 int timer_delete(timer_t timerid);
diff --git a/lib/posix/clock.c b/lib/posix/clock.c
index 1798157451a..d179243c573 100644
--- a/lib/posix/clock.c
+++ b/lib/posix/clock.c
@@ -57,6 +57,40 @@ int clock_gettime(clockid_t clock_id, struct timespec *ts)
 	return 0;
 }
 
+/**
+ * @brief Set the time of the specified clock.
+ *
+ * See IEEE 1003.1.
+ *
+ * Note that only the `CLOCK_REALTIME` clock can be set using this
+ * call.
+ */
+int clock_settime(clockid_t clock_id, const struct timespec *tp)
+{
+	struct timespec base;
+	int res;
+
+	if (clock_id != CLOCK_REALTIME) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	res = clock_gettime(clock_id, &base);
+	if (res != 0) {
+		return res;
+	}
+
+	s64_t delta = (s64_t)NSEC_PER_SEC * (tp->tv_sec - base.tv_sec) +
+		(tp->tv_nsec - base.tv_nsec);
+
+	base.tv_sec = delta / NSEC_PER_SEC;
+	base.tv_nsec = delta % NSEC_PER_SEC;
+
+	rt_clock_base = base;
+
+	return 0;
+}
+
 /**
  * @brief Get current real time.
  *