diff -r 8428d15cbeff Lib/test/test_sys_settrace.py
--- a/Lib/test/test_sys_settrace.py	Sat Jun 04 07:13:38 2016 +0000
+++ b/Lib/test/test_sys_settrace.py	Sat Jun 04 17:34:25 2016 +0200
@@ -388,6 +388,15 @@
              (257, 'line'),
              (257, 'return')])
 
+    def test_17_none_f_trace(self):
+        # Issue 20041: fix TypeError when f_trace is set to None.
+        def func():
+            sys._getframe().f_trace = None
+            lineno = 2
+        self.run_and_compare(func,
+            [(0, 'call'),
+             (1, 'line')])
+
 
 class RaisingTraceFuncTestCase(unittest.TestCase):
     def setUp(self):
diff -r 8428d15cbeff Objects/frameobject.c
--- a/Objects/frameobject.c	Sat Jun 04 07:13:38 2016 +0000
+++ b/Objects/frameobject.c	Sat Jun 04 17:34:25 2016 +0200
@@ -344,6 +344,8 @@
     /* We rely on f_lineno being accurate when f_trace is set. */
     f->f_lineno = PyFrame_GetLineNumber(f);
 
+    if (v == Py_None)
+        v = NULL;
     Py_XINCREF(v);
     Py_XSETREF(f->f_trace, v);