diff --git a/docs/source/reference.rst b/docs/source/reference.rst
index 2018b84..351e8c1 100644
--- a/docs/source/reference.rst
+++ b/docs/source/reference.rst
@@ -381,3 +381,42 @@ write `stateful tests
 <https://hypothesis.readthedocs.io/en/latest/stateful.html>`__ for
 Trio-based libraries, then check out `hypothesis-trio
 <https://github.com/python-trio/hypothesis-trio>`__.
+
+
+.. _trio-run-config:
+
+Using alternative Trio runners
+------------------------------
+
+If you are working with a library that provides integration with Trio,
+such as via :ref:`guest mode <trio:guest-mode>`, it can be used with
+pytest-trio as well.  Setting ``trio_run`` in the pytest configuration
+makes your choice the global default for both tests explicitly marked
+with ``@pytest.mark.trio`` and those automatically marked by Trio mode.
+``trio_run`` presently supports ``trio`` and ``qtrio``.
+
+.. code-block:: ini
+
+   # pytest.ini
+   [pytest]
+   trio_mode = true
+   trio_run = qtrio
+
+.. code-block:: python
+
+   import pytest
+
+   @pytest.mark.trio
+   async def test():
+       assert True
+
+If you want more granular control or need to use a specific function,
+it can be passed directly to the marker.
+
+.. code-block:: python
+
+   import pytest
+
+   @pytest.mark.trio(run=qtrio.run)
+   async def test():
+       assert True
diff --git a/pytest_trio/_tests/helpers.py b/pytest_trio/_tests/helpers.py
index 5ae5f9e..3715fa5 100644
--- a/pytest_trio/_tests/helpers.py
+++ b/pytest_trio/_tests/helpers.py
@@ -5,11 +5,20 @@ def enable_trio_mode_via_pytest_ini(testdir):
     testdir.makefile(".ini", pytest="[pytest]\ntrio_mode = true\n")
 
 
+def enable_trio_mode_trio_run_via_pytest_ini(testdir):
+    testdir.makefile(
+        ".ini", pytest="[pytest]\ntrio_mode = true\ntrio_run = trio\n"
+    )
+
+
 def enable_trio_mode_via_conftest_py(testdir):
     testdir.makeconftest("from pytest_trio.enable_trio_mode import *")
 
 
 enable_trio_mode = pytest.mark.parametrize(
-    "enable_trio_mode",
-    [enable_trio_mode_via_pytest_ini, enable_trio_mode_via_conftest_py]
+    "enable_trio_mode", [
+        enable_trio_mode_via_pytest_ini,
+        enable_trio_mode_trio_run_via_pytest_ini,
+        enable_trio_mode_via_conftest_py,
+    ]
 )
diff --git a/pytest_trio/_tests/test_fixture_mistakes.py b/pytest_trio/_tests/test_fixture_mistakes.py
index 5521a80..077861d 100644
--- a/pytest_trio/_tests/test_fixture_mistakes.py
+++ b/pytest_trio/_tests/test_fixture_mistakes.py
@@ -146,3 +146,28 @@ async def test_whatever(async_fixture):
 
     result.assert_outcomes(failed=1)
     result.stdout.fnmatch_lines(["*async_fixture*cancelled the test*"])
+
+
+@enable_trio_mode
+def test_too_many_clocks(testdir, enable_trio_mode):
+    enable_trio_mode(testdir)
+
+    testdir.makepyfile(
+        """
+        import pytest
+
+        @pytest.fixture
+        def extra_clock(mock_clock):
+            return mock_clock
+
+        async def test_whatever(mock_clock, extra_clock):
+            pass
+        """
+    )
+
+    result = testdir.runpytest()
+
+    result.assert_outcomes(failed=1)
+    result.stdout.fnmatch_lines(
+        ["*ValueError: too many clocks spoil the broth!*"]
+    )
diff --git a/pytest_trio/_tests/test_trio_mode.py b/pytest_trio/_tests/test_trio_mode.py
index efc66a8..f7bf61f 100644
--- a/pytest_trio/_tests/test_trio_mode.py
+++ b/pytest_trio/_tests/test_trio_mode.py
@@ -36,3 +36,148 @@ def test_trio_mode(testdir, enable_trio_mode):
 
     result = testdir.runpytest()
     result.assert_outcomes(passed=2, failed=2)
+
+
+# This is faking qtrio due to real qtrio's dependence on either
+# PyQt5 or PySide2.  They are both large and require special
+# handling in CI.  The testing here is able to focus on the
+# pytest-trio features with just this minimal substitute.
+qtrio_text = """
+import trio
+
+fake_used = False
+
+def run(*args, **kwargs):
+    global fake_used
+    fake_used = True
+
+    return trio.run(*args, **kwargs)
+"""
+
+
+def test_trio_mode_and_qtrio_run_configuration(testdir):
+    testdir.makefile(
+        ".ini", pytest="[pytest]\ntrio_mode = true\ntrio_run = qtrio\n"
+    )
+
+    testdir.makepyfile(qtrio=qtrio_text)
+
+    test_text = """
+    import qtrio
+    import trio
+
+    async def test_fake_qtrio_used():
+        await trio.sleep(0)
+        assert qtrio.fake_used
+    """
+    testdir.makepyfile(test_text)
+
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=1)
+
+
+def test_trio_mode_and_qtrio_marker(testdir):
+    testdir.makefile(".ini", pytest="[pytest]\ntrio_mode = true\n")
+
+    testdir.makepyfile(qtrio=qtrio_text)
+
+    test_text = """
+    import pytest
+    import qtrio
+    import trio
+
+    @pytest.mark.trio(run=qtrio.run)
+    async def test_fake_qtrio_used():
+        await trio.sleep(0)
+        assert qtrio.fake_used
+    """
+    testdir.makepyfile(test_text)
+
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=1)
+
+
+def test_qtrio_just_run_configuration(testdir):
+    testdir.makefile(".ini", pytest="[pytest]\ntrio_run = qtrio\n")
+
+    testdir.makepyfile(qtrio=qtrio_text)
+
+    test_text = """
+    import pytest
+    import qtrio
+    import trio
+
+    @pytest.mark.trio
+    async def test_fake_qtrio_used():
+        await trio.sleep(0)
+        assert qtrio.fake_used
+    """
+    testdir.makepyfile(test_text)
+
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=1)
+
+
+def test_invalid_trio_run_fails(testdir):
+    run_name = "invalid_trio_run"
+
+    testdir.makefile(
+        ".ini", pytest=f"[pytest]\ntrio_mode = true\ntrio_run = {run_name}\n"
+    )
+
+    test_text = """
+    async def test():
+        pass
+    """
+    testdir.makepyfile(test_text)
+
+    result = testdir.runpytest()
+    result.assert_outcomes()
+    result.stdout.fnmatch_lines(
+        [
+            f"*ValueError: {run_name!r} not valid for 'trio_run' config.  Must be one of: *"
+        ]
+    )
+
+
+def test_closest_explicit_run_wins(testdir):
+    testdir.makefile(
+        ".ini", pytest=f"[pytest]\ntrio_mode = true\ntrio_run = trio\n"
+    )
+    testdir.makepyfile(qtrio=qtrio_text)
+
+    test_text = """
+    import pytest
+    import pytest_trio
+    import qtrio
+
+    @pytest.mark.trio(run='should be ignored')
+    @pytest.mark.trio(run=qtrio.run)
+    async def test():
+        assert qtrio.fake_used
+    """
+    testdir.makepyfile(test_text)
+
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=1)
+
+
+def test_ini_run_wins_with_blank_marker(testdir):
+    testdir.makefile(
+        ".ini", pytest=f"[pytest]\ntrio_mode = true\ntrio_run = qtrio\n"
+    )
+    testdir.makepyfile(qtrio=qtrio_text)
+
+    test_text = """
+    import pytest
+    import pytest_trio
+    import qtrio
+
+    @pytest.mark.trio
+    async def test():
+        assert qtrio.fake_used
+    """
+    testdir.makepyfile(test_text)
+
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=1)
diff --git a/pytest_trio/plugin.py b/pytest_trio/plugin.py
index 12e774b..61c4181 100644
--- a/pytest_trio/plugin.py
+++ b/pytest_trio/plugin.py
@@ -1,4 +1,5 @@
 """pytest-trio implementation."""
+from functools import wraps, partial
 import sys
 from traceback import format_exception
 from collections.abc import Coroutine, Generator
@@ -7,7 +8,8 @@
 import outcome
 import pytest
 import trio
-from trio.testing import MockClock, trio_test
+from trio.abc import Clock, Instrument
+from trio.testing import MockClock
 from async_generator import (
     async_generator, yield_, asynccontextmanager, isasyncgen,
     isasyncgenfunction
@@ -39,6 +41,11 @@ def pytest_addoption(parser):
         type="bool",
         default=False,
     )
+    parser.addini(
+        "trio_run",
+        "what runner should pytest-trio use? [trio, qtrio]",
+        default="trio",
+    )
 
 
 def pytest_configure(config):
@@ -307,8 +314,53 @@ async def run(self, test_ctx, contextvars_ctx):
                     raise RuntimeError("too many yields in fixture")
 
 
+def _trio_test(run):
+    """Use:
+        @trio_test
+        async def test_whatever():
+            await ...
+
+    Also: if a pytest fixture is passed in that subclasses the ``Clock`` abc, then
+    that clock is passed to ``trio.run()``.
+    """
+
+    def decorator(fn):
+        @wraps(fn)
+        def wrapper(**kwargs):
+            __tracebackhide__ = True
+            clocks = [c for c in kwargs.values() if isinstance(c, Clock)]
+            if not clocks:
+                clock = None
+            elif len(clocks) == 1:
+                clock = clocks[0]
+            else:
+                raise ValueError("too many clocks spoil the broth!")
+            instruments = [
+                i for i in kwargs.values() if isinstance(i, Instrument)
+            ]
+            return run(
+                partial(fn, **kwargs), clock=clock, instruments=instruments
+            )
+
+        return wrapper
+
+    return decorator
+
+
 def _trio_test_runner_factory(item, testfunc=None):
-    testfunc = testfunc or item.obj
+    if testfunc:
+        run = trio.run
+    else:
+        testfunc = item.obj
+
+        for marker in item.iter_markers("trio"):
+            maybe_run = marker.kwargs.get('run')
+            if maybe_run is not None:
+                run = maybe_run
+                break
+        else:
+            # no marker found that explicitly specifiers the runner so use config
+            run = choose_run(config=item.config)
 
     if getattr(testfunc, '_trio_test_runner_wrapped', False):
         # We have already wrapped this, perhaps because we combined Hypothesis
@@ -320,7 +372,7 @@ def _trio_test_runner_factory(item, testfunc=None):
             'test function `%r` is marked trio but is not async' % item
         )
 
-    @trio_test
+    @_trio_test(run=run)
     async def _bootstrap_fixtures_and_run_test(**kwargs):
         __tracebackhide__ = True
 
@@ -438,19 +490,36 @@ def pytest_fixture_setup(fixturedef, request):
 ################################################################
 
 
-def automark(items):
+def automark(items, run=trio.run):
     for item in items:
         if hasattr(item.obj, "hypothesis"):
             test_func = item.obj.hypothesis.inner_test
         else:
             test_func = item.obj
         if iscoroutinefunction(test_func):
-            item.add_marker(pytest.mark.trio)
+            item.add_marker(pytest.mark.trio(run=run))
+
+
+def choose_run(config):
+    run_string = config.getini("trio_run")
+
+    if run_string == "trio":
+        run = trio.run
+    elif run_string == "qtrio":
+        import qtrio
+        run = qtrio.run
+    else:
+        raise ValueError(
+            f"{run_string!r} not valid for 'trio_run' config." +
+            "  Must be one of: trio, qtrio"
+        )
+
+    return run
 
 
 def pytest_collection_modifyitems(config, items):
     if config.getini("trio_mode"):
-        automark(items)
+        automark(items, run=choose_run(config=config))
 
 
 ################################################################