diff --git a/changelog.d/2497.change.rst b/changelog.d/2497.change.rst
new file mode 100644
index 00000000000..91d840f7a77
--- /dev/null
+++ b/changelog.d/2497.change.rst
@@ -0,0 +1 @@
+Officially deprecated PEP 440 non-compliant versions.
diff --git a/pkg_resources/__init__.py b/pkg_resources/__init__.py
index c84f1dd9e89..3aafe6525c3 100644
--- a/pkg_resources/__init__.py
+++ b/pkg_resources/__init__.py
@@ -113,6 +113,11 @@ def parse_version(v):
     try:
         return packaging.version.Version(v)
     except packaging.version.InvalidVersion:
+        warnings.warn(
+            f"{v} is an invalid version and will not be supported in "
+            "a future release",
+            PkgResourcesDeprecationWarning,
+        )
         return packaging.version.LegacyVersion(v)
 
 
diff --git a/pytest.ini b/pytest.ini
index bdcab1bffb8..2678afd8466 100644
--- a/pytest.ini
+++ b/pytest.ini
@@ -31,3 +31,6 @@ filterwarnings=
 	# https://github.com/pypa/setuptools/issues/917
 	ignore:setup.py install is deprecated.
 	ignore:easy_install command is deprecated.
+
+	# https://github.com/pypa/setuptools/issues/2497
+	ignore:.* is an invalid version and will not be supported::pkg_resources