diff --git a/docs/api.rst b/docs/api.rst
index db39ad99..917fc627 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -383,6 +383,9 @@ Connection Methods
     the root PID of a running Docker, LXC, LXD, or systemd-nspawn
     container.
 
+    The setns method depends on the built-in :mod:`ctypes` module, and thus
+    does not support Python 2.4.
+
     A program is required only to find the root PID, after which management
     of the child Python interpreter is handled directly.
 
diff --git a/tests/setns_test.py b/tests/setns_test.py
index b8a75788..d48179b1 100644
--- a/tests/setns_test.py
+++ b/tests/setns_test.py
@@ -1,6 +1,7 @@
 
 import os
 import socket
+import sys
 
 import mitogen
 import mitogen.parent
@@ -34,5 +35,12 @@ class DockerTest(testlib.DockerMixin, testlib.TestCase):
             via_setns.call(socket.gethostname),
         )
 
+
+DockerTest = unittest2.skipIf(
+    condition=sys.version_info < (2, 5),
+    reason="mitogen.setns unsupported on Python <2.4"
+)(DockerTest)
+
+
 if __name__ == '__main__':
     unittest2.main()