Index: Lib/test/regrtest.py
===================================================================
--- Lib/test/regrtest.py	(revision 87131)
+++ Lib/test/regrtest.py	(working copy)
@@ -906,11 +906,17 @@
             yield name, getattr(self, get_name), getattr(self, restore_name)
 
     def __enter__(self):
+        self.saved_modules = sys.modules.copy()
         self.saved_values = dict((name, get()) for name, get, restore
                                                    in self.resource_info())
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
+        saved_modules = self.saved_modules
+        del self.saved_modules
+        sys.modules.clear()
+        sys.modules.update(saved_modules)
+
         saved_values = self.saved_values
         del self.saved_values
         for name, get, restore in self.resource_info():