diff --git a/bin/tests/system/inline/ns8/named.conf.in b/bin/tests/system/inline/ns8/named.conf.in
index 242c4dc870..b6ee1bf16a 100644
--- a/bin/tests/system/inline/ns8/named.conf.in
+++ b/bin/tests/system/inline/ns8/named.conf.in
@@ -151,3 +151,10 @@ zone example {
 	auto-dnssec maintain;
 	file "example.db";
 };
+
+zone "unsigned-serial-test" {
+	type primary;
+	inline-signing yes;
+	auto-dnssec maintain;
+	file "unsigned-serial-test.db";
+};
diff --git a/bin/tests/system/inline/ns8/sign.sh b/bin/tests/system/inline/ns8/sign.sh
index 9033c72079..d8702fd2bc 100755
--- a/bin/tests/system/inline/ns8/sign.sh
+++ b/bin/tests/system/inline/ns8/sign.sh
@@ -21,12 +21,13 @@ do
   keyname=`$KEYGEN -q -a $DEFAULT_ALGORITHM -b $DEFAULT_BITS -n zone $zone`
   keyname=`$KEYGEN -q -a $DEFAULT_ALGORITHM -b $DEFAULT_BITS -n zone -f KSK $zone`
   cp example.com.db.in ${zone}.db
-  $SIGNER -S -T 3600 -O raw -o ${zone} ${zone}.db > /dev/null 2>&1
+  $SIGNER -S -T 3600 -O raw -L 2000042407 -o ${zone} ${zone}.db > /dev/null 2>&1
 done
 
-zone=example
-rm -f K${zone}.+*+*.key
-rm -f K${zone}.+*+*.private
-keyname=`$KEYGEN -q -a $DEFAULT_ALGORITHM -b $DEFAULT_BITS -n zone $zone`
-keyname=`$KEYGEN -q -a $DEFAULT_ALGORITHM -b $DEFAULT_BITS -n zone -f KSK $zone`
-cp ${zone}.db.in ${zone}.db
+for zone in example unsigned-serial-test; do
+  rm -f K${zone}.+*+*.key
+  rm -f K${zone}.+*+*.private
+  keyname=`$KEYGEN -q -a $DEFAULT_ALGORITHM -b $DEFAULT_BITS -n zone $zone`
+  keyname=`$KEYGEN -q -a $DEFAULT_ALGORITHM -b $DEFAULT_BITS -n zone -f KSK $zone`
+  cp example.db.in ${zone}.db
+done
diff --git a/bin/tests/system/inline/tests_signed_zone_files.py b/bin/tests/system/inline/tests_signed_zone_files.py
new file mode 100755
index 0000000000..0abbb987be
--- /dev/null
+++ b/bin/tests/system/inline/tests_signed_zone_files.py
@@ -0,0 +1,68 @@
+############################################################################
+# Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# See the COPYRIGHT file distributed with this work for additional
+# information regarding copyright ownership.
+############################################################################
+
+import glob
+import struct
+
+
+class RawFormatHeader(dict):
+    '''
+    A dictionary of raw-format header fields read from a zone file.
+    '''
+
+    fields = [
+        'format',
+        'version',
+        'dumptime',
+        'flags',
+        'sourceserial',
+        'lastxfrin',
+    ]
+
+    def __init__(self, file_name):
+        header = struct.Struct('>IIIIII')
+        with open(file_name, 'rb') as data:
+            header_data = data.read(header.size)
+        super().__init__(zip(self.fields, header.unpack_from(header_data)))
+
+
+def test_unsigned_serial_number():
+
+    '''
+    Check whether all signed zone files in the "ns8" subdirectory contain the
+    serial number of the unsigned version of the zone in the raw-format header.
+    The test assumes that all "*.signed" files in the "ns8" subdirectory are in
+    raw format.
+
+    Notes:
+
+      - The actual zone signing and dumping happens while the tests.sh phase of
+        the "inline" system test is set up and run.  This check only verifies
+        the outcome of those events; it does not initiate any signing or
+        dumping itself.
+
+      - example[0-9][0-9].com.db.signed files are initially signed by
+        dnssec-signzone while the others - by named.
+    '''
+
+    zones_with_unsigned_serial_missing = []
+
+    for signed_zone in sorted(glob.glob('ns8/*.signed')):
+        raw_header = RawFormatHeader(signed_zone)
+        # Ensure the unsigned serial number is placed where it is expected.
+        assert raw_header['format'] == 2
+        assert raw_header['version'] == 1
+        # Check whether the header flags indicate that the unsigned serial
+        # number is set and that the latter is indeed set.
+        if raw_header['flags'] & 0x02 == 0 or raw_header['sourceserial'] == 0:
+            zones_with_unsigned_serial_missing.append(signed_zone)
+
+    assert not zones_with_unsigned_serial_missing
diff --git a/util/copyrights b/util/copyrights
index e57b83189e..b1752be8ce 100644
--- a/util/copyrights
+++ b/util/copyrights
@@ -426,6 +426,7 @@
 ./bin/tests/system/inline/ns8/sign.sh		SH	2020,2021,2022
 ./bin/tests/system/inline/setup.sh		SH	2011,2012,2013,2014,2016,2017,2018,2019,2020,2021,2022
 ./bin/tests/system/inline/tests.sh		SH	2011,2012,2013,2014,2016,2017,2018,2019,2020,2021,2022
+./bin/tests/system/inline/tests_signed_zone_files.py	PYTHON	2022
 ./bin/tests/system/integrity/clean.sh		SH	2017,2018,2019,2020,2021,2022
 ./bin/tests/system/integrity/setup.sh		SH	2018,2019,2020,2021,2022
 ./bin/tests/system/integrity/tests.sh		SH	2017,2018,2019,2020,2021,2022