diff --git a/Lib/test/test_tcl.py b/Lib/test/test_tcl.py
index c0c6341c928..d12fb224849 100644
--- a/Lib/test/test_tcl.py
+++ b/Lib/test/test_tcl.py
@@ -376,6 +376,7 @@ class TclTest(unittest.TestCase):
             result = arg
             return arg
         self.interp.createcommand('testfunc', testfunc)
+        self.addCleanup(self.interp.tk.deletecommand, 'testfunc')
         def check(value, expected, eq=self.assertEqual):
             r = self.interp.call('testfunc', value)
             self.assertIsInstance(result, str)
diff --git a/Misc/NEWS b/Misc/NEWS
index d469f689c03..dafdb3f7792 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -17,6 +17,11 @@ Library
 - Issue #19748: On AIX, time.mktime() now raises an OverflowError for year
   outsize range [1902; 2037].
 
+Tests
+-----
+
+- Issue #20743: Fix a reference leak in test_tcl.
+
 
 What's New in Python 3.4.0 release candidate 2?
 ===============================================