diff --git a/Lib/runpy.py b/Lib/runpy.py
index d2f18d3..4e8d563 100755
--- a/Lib/runpy.py
+++ b/Lib/runpy.py
@@ -21,8 +21,9 @@
 ]
 
 
-def _run_code(code, run_globals, init_globals,
-              mod_name, mod_fname, mod_loader):
+def _run_code(code, run_globals, init_globals=None,
+              mod_name=None, mod_fname=None,
+              mod_loader=None):
     """Helper for _run_module_code"""
     if init_globals is not None:
         run_globals.update(init_globals)
@@ -34,35 +35,30 @@
 
 def _run_module_code(code, init_globals=None,
                     mod_name=None, mod_fname=None,
-                    mod_loader=None, alter_sys=False):
+                    mod_loader=None):
     """Helper for run_module"""
     # Set up the top level namespace dictionary
-    if alter_sys:
-        # Modify sys.argv[0] and sys.module[mod_name]
-        temp_module = imp.new_module(mod_name)
-        mod_globals = temp_module.__dict__
-        saved_argv0 = sys.argv[0]
-        restore_module = mod_name in sys.modules
-        if restore_module:
-            saved_module = sys.modules[mod_name]
-        sys.argv[0] = mod_fname
-        sys.modules[mod_name] = temp_module
-        try:
-            _run_code(code, mod_globals, init_globals,
-                      mod_name, mod_fname, mod_loader)
-        finally:
-            sys.argv[0] = saved_argv0
+    temp_module = imp.new_module(mod_name)
+    mod_globals = temp_module.__dict__
+    # Modify sys.argv[0] and sys.module[mod_name]
+    saved_argv0 = sys.argv[0]
+    restore_module = mod_name in sys.modules
+    if restore_module:
+        saved_module = sys.modules[mod_name]
+    sys.argv[0] = mod_fname
+    sys.modules[mod_name] = temp_module
+    try:
+        _run_code(code, mod_globals, init_globals,
+                    mod_name, mod_fname, mod_loader)
+    finally:
+        sys.argv[0] = saved_argv0
         if restore_module:
             sys.modules[mod_name] = saved_module
         else:
             del sys.modules[mod_name]
-        # Copy the globals of the temporary module, as they
-        # may be cleared when the temporary module goes away
-        return mod_globals.copy()
-    else:
-        # Leave the sys module alone
-        return _run_code(code, {}, init_globals,
-                         mod_name, mod_fname, mod_loader)
+    # Copy the globals of the temporary module, as they
+    # may be cleared when the temporary module goes away
+    return mod_globals.copy()
 
 
 # This helper is needed due to a missing component in the PEP 302
@@ -75,13 +71,8 @@
     else:
         return get_filename(mod_name)
 
-
-def run_module(mod_name, init_globals=None,
-                         run_name=None, alter_sys=False):
-    """Execute a module's code without importing it
-
-       Returns the resulting top level namespace dictionary
-    """
+# Helper to get the loader, code and filename for a module
+def _get_module_details(mod_name):
     loader = get_loader(mod_name)
     if loader is None:
         raise ImportError("No module named %s" % mod_name)
@@ -92,10 +83,40 @@
     if code is None:
         raise ImportError("No code object available for %s" % mod_name)
     filename = _get_filename(loader, mod_name)
+    return loader, code, filename
+
+
+# XXX ncoghlan: Should this be documented and made public?
+def _run_module_as_main(mod_name, set_argv0=True):
+    """Runs the designated module in the __main__ namespace
+
+       These __*__ magic variables will be overwritten:
+           __file__
+           __loader__
+    """
+    loader, code, fname = _get_module_details(mod_name)
+    main_globals = sys.modules["__main__"].__dict__
+    if set_argv0:
+        sys.argv[0] = fname
+    return _run_code(code, main_globals, None,
+                     "__main__", fname, loader)
+
+def run_module(mod_name, init_globals=None,
+               run_name=None, alter_sys=False):
+    """Execute a module's code without importing it
+
+       Returns the resulting top level namespace dictionary
+    """
+    loader, code, fname = _get_module_details(mod_name)
     if run_name is None:
         run_name = mod_name
-    return _run_module_code(code, init_globals, run_name,
-                            filename, loader, alter_sys)
+    if alter_sys:
+        return _run_module_code(code, init_globals, run_name,
+                                fname, loader)
+    else:
+        # Leave the sys module alone
+        return _run_code(code, {}, init_globals,
+                         run_name, fname, loader)
 
 
 if __name__ == "__main__":
@@ -104,4 +125,4 @@
         print >> sys.stderr, "No module specified for execution"
     else:
         del sys.argv[0] # Make the requested module sys.argv[0]
-        run_module(sys.argv[0], run_name="__main__", alter_sys=True)
+        _run_module_as_main(sys.argv[0])