diff --git a/pcapkit/utilities/warnings.py b/pcapkit/utilities/warnings.py
index 9beea5758e..1364fd812b 100644
--- a/pcapkit/utilities/warnings.py
+++ b/pcapkit/utilities/warnings.py
@@ -483,7 +483,10 @@ def _importer_stacklevel() -> 'int':
     level then runs past the outermost frame, and the warning is attributed to
     ``<sys>:0``. This counts frames as :func:`warnings.warn` does, and
     :mod:`logging` does from Python 3.11; on earlier versions the log record is
-    attributed to a frame inside the import.
+    attributed to a frame inside the import. GraalPy names the bootstrap's frames
+    ``<frozen _frozen_importlib>`` and ``<frozen _frozen_importlib_external>``,
+    which its :func:`warnings.warn` leaves out too, so those are not counted
+    either (:issue:`1963`).
 
     """
     pcapkit = f'{os.path.sep}pcapkit{os.path.sep}'
@@ -493,7 +496,8 @@ def _importer_stacklevel() -> 'int':
         frame = frame.f_back if frame is not None else None  # the caller, level 1
         while frame is not None:
             filename = frame.f_code.co_filename
-            if not ('importlib' in filename and '_bootstrap' in filename):
+            graalpy_bootstrap = filename.startswith('<frozen _frozen_importlib')
+            if not ('importlib' in filename and ('_bootstrap' in filename or graalpy_bootstrap)):
                 level += 1
                 outermost = level
                 if pcapkit in filename:
diff --git a/tests/corekit/test_sentinel_py_abc_1960_unit.py b/tests/corekit/test_sentinel_py_abc_1960_unit.py
index 5a10088226..be528b7f66 100644
--- a/tests/corekit/test_sentinel_py_abc_1960_unit.py
+++ b/tests/corekit/test_sentinel_py_abc_1960_unit.py
@@ -12,7 +12,8 @@
 :class:`PyABCFallbackTests` runs the checks in a child interpreter that really
 takes the fallback. It starts with ``-S``, so that no module but :mod:`io` has
 imported :mod:`abc` yet, drops both from :data:`sys.modules`, blocks ``_abc``
-and imports them again. The child reports whether :class:`abc.ABCMeta` is
+(except on GraalPy, which takes the fallback unaided, #1963), and imports
+them again. The child reports whether :class:`abc.ABCMeta` is
 ``_py_abc``'s and whether ``_collections_abc`` was already loaded, rather than
 trusting the block. :class:`CModuleTests` pins that, under the C module, the
 names let through for ``_py_abc`` are still refused.
@@ -60,7 +61,11 @@
     preloaded = sorted(name for name in ('abc', 'io', '_collections_abc') if name in sys.modules)
     for name in ('abc', 'io'):
         sys.modules.pop(name, None)
-    sys.modules['_abc'] = None
+    # GraalPy's ``_abc`` holds only the two helpers its own ``_py_abc`` imports,
+    # so :mod:`abc` takes the fallback there unaided, and blocking ``_abc``
+    # would break ``_py_abc`` too (#1963).
+    if sys.implementation.name != 'graalpy':
+        sys.modules['_abc'] = None
 
     import abc
     import io  # noqa: F401  # rebuilt on the fallback before anything uses it
diff --git a/tests/test_tier_guard_xdist.py b/tests/test_tier_guard_xdist.py
index cb9fd2ac3e..a07a7c79d1 100644
--- a/tests/test_tier_guard_xdist.py
+++ b/tests/test_tier_guard_xdist.py
@@ -81,6 +81,12 @@
 #: Test tier (#1958): checks the guard in xdist workers on each leg's interpreter.
 __tier__ = 'ALL'
 
+#: Why the nested-session probes skip GraalPy (#1963): each starts a whole
+#: ``pytest -n`` session of fresh GraalPy interpreters, which took minutes a test
+#: on the experimental leg while the other workers idled. What they pin is the
+#: guard's xdist handling, which no interpreter changes, so the CPython legs cover it.
+SKIP_NESTED_ON_GRAALPY = 'a nested pytest-xdist session is too slow on GraalPy (#1963)'
+
 #: Capture name the probe module in :class:`XdistSubprocessTests` reads. Not
 #: tracked by git -- see :func:`tests._tiers.committed_captures` -- so it is a
 #: tier violation regardless of what ``make samples`` has built locally.
@@ -177,6 +183,7 @@ def _child_environ() -> 'dict[str, str]':
 
 @unittest.skipUnless(importlib.util.find_spec('xdist') is not None,
                       'pytest-xdist not installed')
+@unittest.skipIf(sys.implementation.name == 'graalpy', SKIP_NESTED_ON_GRAALPY)
 class XdistSubprocessTests(unittest.TestCase):
     """End-to-end reproduction: a real violation, a real ``pytest`` subprocess.
 
@@ -300,6 +307,7 @@ def pytest_runtest_setup(item):
 
 @unittest.skipUnless(importlib.util.find_spec('xdist') is not None,
                       'pytest-xdist not installed')
+@unittest.skipIf(sys.implementation.name == 'graalpy', SKIP_NESTED_ON_GRAALPY)
 class ProbeWorkerCrashTests(unittest.TestCase):
     """A worker dying mid-probe fails that one test, not the session (#1756).
 
diff --git a/tests/utilities/test_compat.py b/tests/utilities/test_compat.py
index c6bae26df8..d5f1a9e69b 100644
--- a/tests/utilities/test_compat.py
+++ b/tests/utilities/test_compat.py
@@ -158,6 +158,11 @@
 #: assertion is aimed there.
 OWN_MODULE_PREFIX = 'pcapkit'
 
+#: Whether a :exc:`UnicodeDecodeError` row's message is compared past the octet
+#: and position it names. GraalPy's codecs word the reason their own way --
+#: ``malformed input`` for the rows below -- so there the reason is left out (#1963).
+DECODE_REASON_COMPARED = sys.implementation.name != 'graalpy'
+
 #: ``(value, encoding, errors, outcome)`` for ``compat.unquote``, each as Python
 #: 3.9's :func:`urllib.parse.unquote` has it: the text returned, or the exception
 #: type and message raised. ``None`` keywords leave the defaults in place. Before
@@ -340,7 +345,11 @@ def assert_unquotes_as_python39(self, unquote: 'Callable[..., str]') -> None:
                 else:
                     with self.assertRaises(outcome[0]) as raised:
                         unquote(value, **kwargs)
-                    self.assertEqual(str(raised.exception), outcome[1])
+                    message, expected = str(raised.exception), outcome[1]
+                    if outcome[0] is UnicodeDecodeError and not DECODE_REASON_COMPARED:
+                        message = message.rpartition(': ')[0]
+                        expected = expected.rpartition(': ')[0]
+                    self.assertEqual(message, expected)
 
     def test_unquote_decodes_bytes_as_python39_does(self) -> None:
         """From 3.9 the name is :func:`urllib.parse.unquote` itself (#1693)."""
diff --git a/tests/utilities/test_config_unit.py b/tests/utilities/test_config_unit.py
index 78d0b833ea..ab01446e9c 100644
--- a/tests/utilities/test_config_unit.py
+++ b/tests/utilities/test_config_unit.py
@@ -590,5 +590,47 @@ def test_an_error_filter_makes_the_import_raise(self) -> None:
                 self.assertIn(f"ConfigWarning: PCAPKIT_{name}={text!r}", result.stderr)
 
 
+class ImporterStacklevelTests(unittest.TestCase):
+    """GitHub issue #1963: the importer's level leaves out the bootstrap, however it is named.
+
+    CPython names :mod:`importlib`'s bootstrap frames ``<frozen importlib._bootstrap>``
+    and ``<frozen importlib._bootstrap_external>``, GraalPy ``<frozen _frozen_importlib>``
+    and ``<frozen _frozen_importlib_external>``, and each one's :func:`warnings.warn`
+    leaves its own out. Counting GraalPy's ran the level past the outermost frame,
+    so the import-time warnings above named ``<sys>:0`` there.
+
+    """
+
+    def level_under(self, bootstrap: str) -> int:
+        """The level a :mod:`pcapkit` frame gets, imported through ``bootstrap`` frames.
+
+        The chain is that of an import: this test, a bootstrap frame, a package
+        body, a bootstrap frame, then the reporting module. Leaving the bootstrap
+        out, the test is the third frame.
+
+        """
+        pcapkit_warnings = importlib.import_module('pcapkit.utilities.warnings')
+        namespace = {'_importer_stacklevel': getattr(pcapkit_warnings, '_importer_stacklevel')}
+        package = os.path.join(os.sep, 'site-packages', 'pcapkit', 'probe_1963.py')
+        reporter = ('def report():\n    return _importer_stacklevel()\n'
+                    'def body():\n    return load_inner()\n')
+        importer = ('def load_inner():\n    return report()\n'
+                    'def load_outer():\n    return body()\n')
+        exec(compile(reporter, package, 'exec'), namespace)  # nosec: B102  # pylint: disable=exec-used
+        exec(compile(importer, bootstrap, 'exec'), namespace)  # nosec: B102  # pylint: disable=exec-used
+        return namespace['load_outer']()
+
+    def test_each_interpreters_bootstrap_frames_are_left_out(self) -> None:
+        """Both CPython's names and GraalPy's leave the test the third frame."""
+        for bootstrap in ('<frozen importlib._bootstrap>', '<frozen importlib._bootstrap_external>',
+                          '<frozen _frozen_importlib>', '<frozen _frozen_importlib_external>'):
+            with self.subTest(bootstrap=bootstrap):
+                self.assertEqual(self.level_under(bootstrap), 3)
+
+    def test_any_other_frame_is_counted(self) -> None:
+        """The control: frames named otherwise are counted, so the level is one further out."""
+        self.assertEqual(self.level_under('<string>'), 4)
+
+
 if __name__ == '__main__':
     unittest.main()