diff --git a/changelog/5023.feature.rst b/changelog/5023.feature.rst
index a4c67fe68..348e2f1c3 100644
--- a/changelog/5023.feature.rst
+++ b/changelog/5023.feature.rst
@@ -1 +1,5 @@
-``--strict`` is now called ``--strict-markers`` as it is more explicit about what it does. The old name still works for backward compatibility.
+New flag ``--strict-markers`` that triggers an error when unknown markers (e.g. those not registered using the `markers option`_ in the configuration file) are used in the test suite.
+
+The existing ``--strict`` option has the same behavior currently, but can be augmented in the future for additional checks.
+
+.. _`markers option`: https://docs.pytest.org/en/latest/reference.html#confval-markers
diff --git a/doc/en/reference.rst b/doc/en/reference.rst
index 4b76bdaf7..33e4412ca 100644
--- a/doc/en/reference.rst
+++ b/doc/en/reference.rst
@@ -1261,8 +1261,8 @@ passed multiple times. The expected format is ``name=value``. For example::
 
 .. confval:: markers
 
-    When the ``--strict-markers`` command-line argument is used, only known markers -
-    defined in code by core pytest or some plugin - are allowed.
+    When the ``--strict-markers`` or ``--strict`` command-line arguments are used,
+    only known markers - defined in code by core pytest or some plugin - are allowed.
 
     You can list additional markers in this setting to add them to the whitelist,
     in which case you probably want to add ``--strict-markers`` to ``addopts``
@@ -1276,9 +1276,6 @@ passed multiple times. The expected format is ``name=value``. For example::
             slow
             serial
 
-    **Note**: This option was previously called ``--strict``, which is now an
-    alias preserved for backward compatibility.
-
 .. confval:: minversion
 
    Specifies a minimal pytest version required for running tests.
diff --git a/testing/code/test_excinfo.py b/testing/code/test_excinfo.py
index 92e9395c7..a76797301 100644
--- a/testing/code/test_excinfo.py
+++ b/testing/code/test_excinfo.py
@@ -11,7 +11,6 @@ import textwrap
 import py
 import six
 from six.moves import queue
-from test_source import astonly
 
 import _pytest
 import pytest
@@ -147,7 +146,6 @@ class TestTraceback_f_g_h(object):
         assert s.startswith("def f():")
         assert s.endswith("raise ValueError")
 
-    @astonly
     @failsonjython
     def test_traceback_entry_getsource_in_construct(self):
         source = _pytest._code.Source(
diff --git a/testing/code/test_source.py b/testing/code/test_source.py
index aa56273c4..8d400a289 100644
--- a/testing/code/test_source.py
+++ b/testing/code/test_source.py
@@ -16,7 +16,6 @@ import _pytest._code
 import pytest
 from _pytest._code import Source
 
-astonly = pytest.mark.nothing
 failsonjython = pytest.mark.xfail("sys.platform.startswith('java')")
 
 
@@ -227,7 +226,6 @@ class TestSourceParsingAndCompiling(object):
         s = source.getstatement(1)
         assert s == str(source)
 
-    @astonly
     def test_getstatementrange_within_constructs(self):
         source = Source(
             """\
@@ -630,7 +628,6 @@ x = 3
 
 
 class TestTry(object):
-    pytestmark = astonly
     source = """\
 try:
     raise ValueError
@@ -675,7 +672,6 @@ finally:
 
 
 class TestIf(object):
-    pytestmark = astonly
     source = """\
 if 1:
     y = 3
diff --git a/testing/test_mark.py b/testing/test_mark.py
index 03cd2f78c..b2f893438 100644
--- a/testing/test_mark.py
+++ b/testing/test_mark.py
@@ -44,11 +44,11 @@ class TestMark(object):
         class SomeClass(object):
             pass
 
-        assert pytest.mark.fun(some_function) is some_function
-        assert pytest.mark.fun.with_args(some_function) is not some_function
+        assert pytest.mark.foo(some_function) is some_function
+        assert pytest.mark.foo.with_args(some_function) is not some_function
 
-        assert pytest.mark.fun(SomeClass) is SomeClass
-        assert pytest.mark.fun.with_args(SomeClass) is not SomeClass
+        assert pytest.mark.foo(SomeClass) is SomeClass
+        assert pytest.mark.foo.with_args(SomeClass) is not SomeClass
 
     def test_pytest_mark_name_starts_with_underscore(self):
         mark = Mark()
@@ -936,11 +936,11 @@ def test_mark_expressions_no_smear(testdir):
 
 def test_addmarker_order():
     node = Node("Test", config=mock.Mock(), session=mock.Mock(), nodeid="Test")
-    node.add_marker("a")
-    node.add_marker("b")
-    node.add_marker("c", append=False)
+    node.add_marker("foo")
+    node.add_marker("bar")
+    node.add_marker("baz", append=False)
     extracted = [x.name for x in node.iter_markers()]
-    assert extracted == ["c", "a", "b"]
+    assert extracted == ["baz", "foo", "bar"]
 
 
 @pytest.mark.filterwarnings("ignore")
diff --git a/tox.ini b/tox.ini
index e9517b63c..fb4134d17 100644
--- a/tox.ini
+++ b/tox.ini
@@ -141,7 +141,7 @@ commands = python scripts/release.py {posargs}
 
 [pytest]
 minversion = 2.0
-addopts = -ra -p pytester
+addopts = -ra -p pytester --strict-markers
 rsyncdirs = tox.ini doc src testing
 python_files = test_*.py *_test.py testing/*/*.py
 python_classes = Test Acceptance
@@ -172,6 +172,11 @@ filterwarnings =
     ignore::_pytest.warning_types.PytestUnknownMarkWarning
 pytester_example_dir = testing/example_scripts
 markers =
+    # dummy markers for testing
+    foo
+    bar
+    baz
+    # conftest.py reorders tests moving slow ones to the end of the list
     slow
 
 [flake8]