diff --git a/test/integration-tests/TEST-04-JOURNAL/TEST-04-JOURNAL.units/logs-filtering.service b/test/integration-tests/TEST-04-JOURNAL/TEST-04-JOURNAL.units/logs-filtering.service
index 4c430058cf..6eca47d1fa 100644
--- a/test/integration-tests/TEST-04-JOURNAL/TEST-04-JOURNAL.units/logs-filtering.service
+++ b/test/integration-tests/TEST-04-JOURNAL/TEST-04-JOURNAL.units/logs-filtering.service
@@ -3,9 +3,8 @@ Description=Log filtering unit
 
 [Service]
 Type=oneshot
-ExecStart=sh -c 'echo "Logging from the service, and ~more~ foo bar"'
 # If the service finishes extremely fast, journald cannot find the source of the
 # stream. Hence, we need to call 'journalctl --sync' before service finishes.
-ExecStart=journalctl --sync
+ExecStart=sh -c 'echo "Logging from the service, and ~more~ foo bar"; journalctl --sync'
 SyslogLevel=notice
 LogLevelMax=info
diff --git a/test/units/TEST-04-JOURNAL.LogFilterPatterns.sh b/test/units/TEST-04-JOURNAL.LogFilterPatterns.sh
index ec99b86226..79482d6078 100755
--- a/test/units/TEST-04-JOURNAL.LogFilterPatterns.sh
+++ b/test/units/TEST-04-JOURNAL.LogFilterPatterns.sh
@@ -3,13 +3,17 @@
 set -eux
 set -o pipefail
 
+# shellcheck source=test/units/util.sh
+. "$(dirname "$0")"/util.sh
+
 if ! cgroupfs_supports_user_xattrs; then
     echo "CGroup does not support user xattrs, skipping LogFilterPatterns= tests."
     exit 0
 fi
 
-# shellcheck source=test/units/util.sh
-. "$(dirname "$0")"/util.sh
+# Unfortunately, journalctl -I/--invocation= is unstable when debug logging is enabled on service manager.
+SAVED_LOG_LEVEL=$(systemctl log-level)
+systemctl log-level info
 
 NEEDS_RELOAD=
 
@@ -25,17 +29,14 @@ add_logs_filtering_override() {
 
 run_service_and_fetch_logs() {
     local unit="${1:?}"
-    local start
 
     if [[ -n "$NEEDS_RELOAD" ]]; then
         systemctl daemon-reload
         NEEDS_RELOAD=
     fi
 
-    journalctl --sync
-    start="$(date '+%Y-%m-%d %T.%6N')"
     systemctl start "$unit"
-    journalctl -q -u "$unit" -S "$start" -p notice
+    journalctl -q -u "$unit" -I -p notice
 }
 
 at_exit() {
@@ -91,3 +92,5 @@ add_logs_filtering_override "delegated-cgroup-filtering.service" "00-allow-all"
 
 add_logs_filtering_override "delegated-cgroup-filtering.service" "01-discard-hello" "~hello"
 [[ -z $(run_service_and_fetch_logs "delegated-cgroup-filtering.service") ]]
+
+systemctl log-level "$SAVED_LOG_LEVEL"
diff --git a/test/units/delegated_cgroup_filtering_payload.sh b/test/units/delegated_cgroup_filtering_payload.sh
index 1181fbb910..6084ae8dcb 100755
--- a/test/units/delegated_cgroup_filtering_payload.sh
+++ b/test/units/delegated_cgroup_filtering_payload.sh
@@ -6,4 +6,7 @@ mkdir /sys/fs/cgroup/system.slice/delegated-cgroup-filtering.service/the_child
 
 echo "parent_process: hello, world!"
 echo "parent_process: hello, people!"
-sleep 2
+
+# If the service finishes extremely fast, journald cannot find the source of the
+# stream. Hence, we need to call 'journalctl --sync' before service finishes.
+journalctl --sync