diff --git a/bin/tests/system/fetchlimit/tests_sh_fetchlimit.py b/bin/tests/system/fetchlimit/tests_sh_fetchlimit.py
index 6df4441b91..04d3e3bf39 100644
--- a/bin/tests/system/fetchlimit/tests_sh_fetchlimit.py
+++ b/bin/tests/system/fetchlimit/tests_sh_fetchlimit.py
@@ -9,6 +9,9 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
+import isctest.mark
 
+
+@isctest.mark.flaky(max_runs=2)
 def test_fetchlimit(run_tests_sh):
     run_tests_sh()
diff --git a/bin/tests/system/isctest/__init__.py b/bin/tests/system/isctest/__init__.py
index 3ea82a3f45..047ca7762a 100644
--- a/bin/tests/system/isctest/__init__.py
+++ b/bin/tests/system/isctest/__init__.py
@@ -14,3 +14,8 @@ from . import instance
 from . import query
 from . import rndc
 from . import log
+
+# isctest.mark module is intentionally NOT imported, because it relies on
+# environment variables which might not be set at the time of import of the
+# `isctest` package. To use the marks, manual `import isctest.mark` is needed
+# instead.
diff --git a/bin/tests/system/pytest_custom_markers.py b/bin/tests/system/isctest/mark.py
similarity index 97%
rename from bin/tests/system/pytest_custom_markers.py
rename to bin/tests/system/isctest/mark.py
index ba3a9d4894..769abbbb5d 100644
--- a/bin/tests/system/pytest_custom_markers.py
+++ b/bin/tests/system/isctest/mark.py
@@ -43,7 +43,7 @@ have_json_c = pytest.mark.skipif(
 
 
 try:
-    import flaky as flaky_pkg
+    import flaky as flaky_pkg  # type: ignore
 except ModuleNotFoundError:
     # In case the flaky package is not installed, run the tests as usual
     # without any attempts to re-run them.
diff --git a/bin/tests/system/nsupdate/tests_sh_nsupdate.py b/bin/tests/system/nsupdate/tests_sh_nsupdate.py
index 5c1a9c7e3d..305f1a191f 100644
--- a/bin/tests/system/nsupdate/tests_sh_nsupdate.py
+++ b/bin/tests/system/nsupdate/tests_sh_nsupdate.py
@@ -11,12 +11,12 @@
 
 import platform
 
-import pytest_custom_markers
+import isctest.mark
 
 
 MAX_RUNS = 2 if platform.system() == "FreeBSD" else 1  # GL#3846
 
 
-@pytest_custom_markers.flaky(max_runs=MAX_RUNS)
+@isctest.mark.flaky(max_runs=MAX_RUNS)
 def test_nsupdate(run_tests_sh):
     run_tests_sh()
diff --git a/bin/tests/system/qmin/tests_sh_qmin.py b/bin/tests/system/qmin/tests_sh_qmin.py
index 607732232e..0faeebd0e9 100644
--- a/bin/tests/system/qmin/tests_sh_qmin.py
+++ b/bin/tests/system/qmin/tests_sh_qmin.py
@@ -9,10 +9,10 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
-import pytest_custom_markers
+import isctest.mark
 
 
 # The qmin test is inherently unstable, see GL #904 for details.
-@pytest_custom_markers.flaky(max_runs=3)
+@isctest.mark.flaky(max_runs=3)
 def test_qmin(run_tests_sh):
     run_tests_sh()
diff --git a/bin/tests/system/reclimit/tests_sh_reclimit.py b/bin/tests/system/reclimit/tests_sh_reclimit.py
index 4710027581..447c9488e0 100644
--- a/bin/tests/system/reclimit/tests_sh_reclimit.py
+++ b/bin/tests/system/reclimit/tests_sh_reclimit.py
@@ -9,10 +9,10 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
-import pytest_custom_markers
+import isctest.mark
 
 
 # The reclimit is known to be quite unstable. GL #1587
-@pytest_custom_markers.flaky(max_runs=2)
+@isctest.mark.flaky(max_runs=2)
 def test_reclimit(run_tests_sh):
     run_tests_sh()
diff --git a/bin/tests/system/rrl/tests_sh_rrl.py b/bin/tests/system/rrl/tests_sh_rrl.py
index 05b43a6fe1..c32305b5d7 100644
--- a/bin/tests/system/rrl/tests_sh_rrl.py
+++ b/bin/tests/system/rrl/tests_sh_rrl.py
@@ -9,10 +9,10 @@
 # See the COPYRIGHT file distributed with this work for additional
 # information regarding copyright ownership.
 
-import pytest_custom_markers
+import isctest.mark
 
 
 # The rrl is known to be quite unstable. GL #172
-@pytest_custom_markers.flaky(max_runs=2)
+@isctest.mark.flaky(max_runs=2)
 def test_rrl(run_tests_sh):
     run_tests_sh()
diff --git a/bin/tests/system/statschannel/tests_json.py b/bin/tests/system/statschannel/tests_json.py
index 4f7c4a7d7c..9b52541847 100755
--- a/bin/tests/system/statschannel/tests_json.py
+++ b/bin/tests/system/statschannel/tests_json.py
@@ -15,12 +15,12 @@ from datetime import datetime
 
 import pytest
 
-import pytest_custom_markers
+import isctest.mark
 
 pytest.register_assert_rewrite("generic")
 import generic
 
-pytestmark = pytest_custom_markers.have_json_c
+pytestmark = isctest.mark.have_json_c
 requests = pytest.importorskip("requests")
 
 
diff --git a/bin/tests/system/statschannel/tests_xml.py b/bin/tests/system/statschannel/tests_xml.py
index 53296155da..81ac187587 100755
--- a/bin/tests/system/statschannel/tests_xml.py
+++ b/bin/tests/system/statschannel/tests_xml.py
@@ -16,12 +16,12 @@ import xml.etree.ElementTree as ET
 
 import pytest
 
-import pytest_custom_markers
+import isctest.mark
 
 pytest.register_assert_rewrite("generic")
 import generic
 
-pytestmark = pytest_custom_markers.have_libxml2
+pytestmark = isctest.mark.have_libxml2
 requests = pytest.importorskip("requests")
 
 
diff --git a/bin/tests/system/timeouts/tests_tcp_timeouts.py b/bin/tests/system/timeouts/tests_tcp_timeouts.py
index 2e2a4b47e2..f615340510 100644
--- a/bin/tests/system/timeouts/tests_tcp_timeouts.py
+++ b/bin/tests/system/timeouts/tests_tcp_timeouts.py
@@ -26,7 +26,7 @@ import dns.query
 import dns.rdataclass
 import dns.rdatatype
 
-import pytest_custom_markers  # pylint: disable=import-error
+import isctest.mark  # pylint: disable=import-error
 
 
 TIMEOUT = 10
@@ -185,7 +185,7 @@ def test_long_axfr(named_port):
         assert soa is not None
 
 
-@pytest_custom_markers.flaky(max_runs=3)
+@isctest.mark.flaky(max_runs=3)
 def test_send_timeout(named_port):
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
         sock.connect(("10.53.0.1", named_port))
@@ -212,7 +212,7 @@ def test_send_timeout(named_port):
                 raise EOFError from e
 
 
-@pytest_custom_markers.long_test
+@isctest.mark.long_test
 def test_max_transfer_idle_out(named_port):
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
         sock.connect(("10.53.0.1", named_port))
@@ -246,7 +246,7 @@ def test_max_transfer_idle_out(named_port):
             assert soa is None
 
 
-@pytest_custom_markers.long_test
+@isctest.mark.long_test
 def test_max_transfer_time_out(named_port):
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
         sock.connect(("10.53.0.1", named_port))