diff --git a/AUTHORS b/AUTHORS
index 0672d4abf..3d050a346 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -200,6 +200,7 @@ Pulkit Goyal
 Punyashloka Biswal
 Quentin Pradet
 Ralf Schmitt
+Ralph Giles
 Ran Benita
 Raphael Castaneda
 Raphael Pierzina
diff --git a/changelog/5416.doc.rst b/changelog/5416.doc.rst
new file mode 100644
index 000000000..81e4c6404
--- /dev/null
+++ b/changelog/5416.doc.rst
@@ -0,0 +1 @@
+Fix PytestUnknownMarkWarning in run/skip example.
diff --git a/doc/en/example/simple.rst b/doc/en/example/simple.rst
index 140f4b840..5e405da56 100644
--- a/doc/en/example/simple.rst
+++ b/doc/en/example/simple.rst
@@ -157,6 +157,10 @@ line option to control skipping of ``pytest.mark.slow`` marked tests:
         )
 
 
+    def pytest_configure(config):
+        config.addinivalue_line("markers", "slow: mark test as slow to run")
+
+
     def pytest_collection_modifyitems(config, items):
         if config.getoption("--runslow"):
             # --runslow given in cli: do not skip slow tests