diff --git a/src/core/timer.c b/src/core/timer.c
index 7f779fb936b..75f1dc1f8be 100644
--- a/src/core/timer.c
+++ b/src/core/timer.c
@@ -346,6 +346,7 @@ static void timer_enter_waiting(Timer *t, bool time_change) {
         bool found_monotonic = false, found_realtime = false;
         bool leave_around = false;
         triple_timestamp ts;
+        dual_timestamp dts;
         TimerValue *v;
         Unit *trigger;
         int r;
@@ -389,10 +390,10 @@ static void timer_enter_waiting(Timer *t, bool time_change) {
 
                         /* To make the delay due to RandomizedDelaySec= work even at boot,
                          * if the scheduled time has already passed, set the time when systemd
-                         * first started as the scheduled time.
-                         * Also, we don't have to check t->persistent since the logic implicitly express true. */
-                        if (v->next_elapse < UNIT(t)->manager->timestamps[MANAGER_TIMESTAMP_USERSPACE].realtime)
-                                v->next_elapse = UNIT(t)->manager->timestamps[MANAGER_TIMESTAMP_USERSPACE].realtime;
+                         * first started as the scheduled time. */
+                        dual_timestamp_from_monotonic(&dts, UNIT(t)->manager->timestamps[MANAGER_TIMESTAMP_USERSPACE].monotonic);
+                        if (v->next_elapse < dts.realtime)
+                                v->next_elapse = dts.realtime;
 
                         if (!found_realtime)
                                 t->next_elapse_realtime = v->next_elapse;
diff --git a/test/TEST-53-ISSUE-16347/Makefile b/test/TEST-53-ISSUE-16347/Makefile
new file mode 120000
index 00000000000..e9f93b1104c
--- /dev/null
+++ b/test/TEST-53-ISSUE-16347/Makefile
@@ -0,0 +1 @@
+../TEST-01-BASIC/Makefile
\ No newline at end of file
diff --git a/test/TEST-53-ISSUE-16347/test.sh b/test/TEST-53-ISSUE-16347/test.sh
new file mode 100755
index 00000000000..089768e8ddb
--- /dev/null
+++ b/test/TEST-53-ISSUE-16347/test.sh
@@ -0,0 +1,11 @@
+#!/usr/bin/env bash
+set -e
+
+TEST_DESCRIPTION="test timer units when initial clock is ahead"
+TEST_NO_NSPAWN=1
+
+future_date=$(date -u +%Y-%m-%dT%H:%M:%S -d '+3 days')
+QEMU_OPTIONS="-rtc base=${future_date}"
+. $TEST_BASE_DIR/test-functions
+
+do_test "$@" 53
diff --git a/test/units/testsuite-53.service b/test/units/testsuite-53.service
new file mode 100644
index 00000000000..d4dd8cc72f8
--- /dev/null
+++ b/test/units/testsuite-53.service
@@ -0,0 +1,7 @@
+[Unit]
+Description=TEST-53-ISSUE-16347
+
+[Service]
+ExecStartPre=rm -f /failed /testok
+ExecStart=/usr/lib/systemd/tests/testdata/units/%N.sh
+Type=oneshot
diff --git a/test/units/testsuite-53.sh b/test/units/testsuite-53.sh
new file mode 100755
index 00000000000..3536c242712
--- /dev/null
+++ b/test/units/testsuite-53.sh
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+set -ex
+set -o pipefail
+
+>/failed
+
+# Reset host date to current time, 3 days in the past.
+date -s "-3 days"
+
+# Run a timer for every 15 minutes.
+systemd-run --unit test-timer --on-calendar "*:0/15:0" true
+
+next_elapsed=$(systemctl show test-timer.timer -p NextElapseUSecRealtime --value)
+next_elapsed=$(date -d "${next_elapsed}" +%s)
+now=$(date +%s)
+time_delta=$((next_elapsed - now))
+
+# Check that the timer will elapse in less than 20 minutes.
+((0 < time_delta && time_delta < 1200)) || {
+    echo 'Timer elapse outside of the expected 20 minute window.'
+    echo "  next_elapsed=${next_elapsed}"
+    echo "  now=${now}"
+    echo "  time_delta=${time_delta}"
+    echo ''
+} >>/failed
+
+if test ! -s /failed ; then
+    rm -f /failed
+    touch /testok
+fi