Issue #21951: Temporary skip crashing test_user_command on AIX.
diff --git a/Lib/test/test_tcl.py b/Lib/test/test_tcl.py
index d8dc9c3..fcbafc5 100644
--- a/Lib/test/test_tcl.py
+++ b/Lib/test/test_tcl.py
@@ -426,6 +426,7 @@
         self.assertEqual(passValue((1, '2', (3.4,))),
                          (1, '2', (3.4,)) if self.wantobjects else '1 2 3.4')
 
+    @unittest.skipIf(sys.platform.startswith("aix"), 'Issue #21951: crashes on AIX')
     def test_user_command(self):
         result = []
         def testfunc(arg):