diff --git a/_pytest/debugging.py b/_pytest/debugging.py
index 1e7dcad5d..6c6bd6a02 100644
--- a/_pytest/debugging.py
+++ b/_pytest/debugging.py
@@ -16,8 +16,6 @@ def pytest_addoption(parser):
         help="start a custom interactive Python debugger on errors. "
              "For example: --pdbcls=IPython.terminal.debugger:TerminalPdb")
 
-def pytest_namespace():
-    return {'set_trace': pytestPDB().set_trace}
 
 def pytest_configure(config):
     if config.getvalue("usepdb_cls"):
@@ -43,25 +41,27 @@ def pytest_configure(config):
     pytestPDB._pdb_cls = pdb_cls
     config._cleanup.append(fin)
 
+
 class pytestPDB(object):
     """ Pseudo PDB that defers to the real pdb. """
     _pluginmanager = None
     _config = None
     _pdb_cls = pdb.Pdb
 
-    def set_trace(self):
+    @classmethod
+    def set_trace(cls):
         """ invoke PDB set_trace debugging, dropping any IO capturing. """
         import _pytest.config
         frame = sys._getframe().f_back
-        if self._pluginmanager is not None:
-            capman = self._pluginmanager.getplugin("capturemanager")
+        if cls._pluginmanager is not None:
+            capman = cls._pluginmanager.getplugin("capturemanager")
             if capman:
                 capman.suspendcapture(in_=True)
-            tw = _pytest.config.create_terminal_writer(self._config)
+            tw = _pytest.config.create_terminal_writer(cls._config)
             tw.line()
             tw.sep(">", "PDB set_trace (IO-capturing turned off)")
-            self._pluginmanager.hook.pytest_enter_pdb(config=self._config)
-        self._pdb_cls().set_trace(frame)
+            cls._pluginmanager.hook.pytest_enter_pdb(config=cls._config)
+        cls._pdb_cls().set_trace(frame)
 
 
 class PdbInvoke(object):
diff --git a/pytest.py b/pytest.py
index 741e2d7f6..d9073f01c 100644
--- a/pytest.py
+++ b/pytest.py
@@ -11,6 +11,7 @@ __all__ = [
     '__version__',
     'register_assert_rewrite',
     'freeze_includes',
+    'set_trace',
 ]
 
 if __name__ == '__main__': # if run as a script or by 'python -m pytest'
@@ -27,7 +28,10 @@ from _pytest.config import (
 from _pytest.assertion import register_assert_rewrite
 from _pytest.freeze_support import freeze_includes
 from _pytest import __version__
+from _pytest.debugging import pytestPDB as __pytestPDB
 
 
+
+set_trace = __pytestPDB.set_trace
+
 _preloadplugins() # to populate pytest.* namespace so help(pytest) works
-