diff --git a/Lib/test/test_unittest.py b/Lib/test/test_unittest.py
index b4716a4..954b40a 100644
--- a/Lib/test/test_unittest.py
+++ b/Lib/test/test_unittest.py
@@ -2096,6 +2096,16 @@
                 'Tests getDescription() for a method with a longer '
                 'docstring.'))
 
+    def testStackFrameTrimming(self):
+        class Frame(object):
+            class tb_frame(object):
+                f_globals = {}
+        result = unittest.TestResult()
+        self.assertFalse(result._is_relevant_tb_level(Frame))
+
+        Frame.tb_frame.f_globals['__unittest'] = True
+        self.assertTrue(result._is_relevant_tb_level(Frame))
+
 classDict = dict(unittest.TestResult.__dict__)
 for m in ('addSkip', 'addExpectedFailure', 'addUnexpectedSuccess',
            '__init__'):
diff --git a/Lib/unittest/__init__.py b/Lib/unittest/__init__.py
index 06fe55d..8f77127 100644
--- a/Lib/unittest/__init__.py
+++ b/Lib/unittest/__init__.py
@@ -64,3 +64,5 @@
 
 # deprecated
 _TextTestResult = TextTestResult
+
+__unittest = True
diff --git a/Lib/unittest/__main__.py b/Lib/unittest/__main__.py
index 5bbda1c..5023610 100644
--- a/Lib/unittest/__main__.py
+++ b/Lib/unittest/__main__.py
@@ -4,5 +4,8 @@
 if sys.argv[0].endswith("__main__.py"):
     sys.argv[0] = "unittest"
 
+__unittest = True
+
+
 from .main import main
 main(module=None)
diff --git a/Lib/unittest/case.py b/Lib/unittest/case.py
index 0d224d8..ac5d1ec 100644
--- a/Lib/unittest/case.py
+++ b/Lib/unittest/case.py
@@ -11,6 +11,8 @@
 from .util import (strclass, safe_repr, sorted_list_difference,
                    unorderable_list_difference)
 
+__unittest = True
+
 
 class SkipTest(Exception):
     """
diff --git a/Lib/unittest/loader.py b/Lib/unittest/loader.py
index 4e9e152..eea5c13 100644
--- a/Lib/unittest/loader.py
+++ b/Lib/unittest/loader.py
@@ -10,6 +10,7 @@
 
 from . import case, suite, util
 
+__unittest = True
 
 # what about .pyc or .pyo (etc)
 # we would need to avoid loading the same tests multiple times
diff --git a/Lib/unittest/main.py b/Lib/unittest/main.py
index e6237b0..e04ec16 100644
--- a/Lib/unittest/main.py
+++ b/Lib/unittest/main.py
@@ -6,6 +6,8 @@
 
 from . import loader, runner
 
+__unittest = True
+
 
 USAGE_AS_MAIN = """\
 Usage: %(progName)s [options] [tests]
diff --git a/Lib/unittest/result.py b/Lib/unittest/result.py
index 746967e..91cf218 100644
--- a/Lib/unittest/result.py
+++ b/Lib/unittest/result.py
@@ -4,6 +4,8 @@
 
 from . import util
 
+__unittest = True
+
 
 class TestResult(object):
     """Holder for test result information.
@@ -98,11 +100,7 @@
         return ''.join(traceback.format_exception(exctype, value, tb))
 
     def _is_relevant_tb_level(self, tb):
-        globs = tb.tb_frame.f_globals
-        is_relevant =  '__name__' in globs and \
-            globs["__name__"].startswith("unittest")
-        del globs
-        return is_relevant
+        return '__unittest' in tb.tb_frame.f_globals
 
     def _count_relevant_tb_levels(self, tb):
         length = 0
diff --git a/Lib/unittest/runner.py b/Lib/unittest/runner.py
index 8773d0c..1729f1d 100644
--- a/Lib/unittest/runner.py
+++ b/Lib/unittest/runner.py
@@ -5,6 +5,8 @@
 
 from . import result
 
+__unittest = True
+
 
 class _WritelnDecorator(object):
     """Used to decorate file-like objects with a handy 'writeln' method"""
diff --git a/Lib/unittest/suite.py b/Lib/unittest/suite.py
index ddd83ae..72b2949 100644
--- a/Lib/unittest/suite.py
+++ b/Lib/unittest/suite.py
@@ -5,6 +5,8 @@
 from . import case
 from . import util
 
+__unittest = True
+
 
 class BaseTestSuite(object):
     """A simple test suite that doesn't provide class or module shared fixtures.
diff --git a/Lib/unittest/util.py b/Lib/unittest/util.py
index 1c1b600..736c202 100644
--- a/Lib/unittest/util.py
+++ b/Lib/unittest/util.py
@@ -1,5 +1,8 @@
 """Various utility functions."""
 
+__unittest = True
+
+
 def safe_repr(obj):
     try:
         return repr(obj)