diff --git a/flake8/pep8.py b/flake8/pep8.py
index bdde37b..766302b 100644
--- a/flake8/pep8.py
+++ b/flake8/pep8.py
@@ -1272,6 +1272,9 @@ def process_options(arglist=None):
             __version__)
     parser = OptionParser(version=version,
                           usage="%prog [options] input ...")
+    parser.add_option('--builtins', default=[], action="append",
+                      help="append builtin function (pyflakes "
+                           "_MAGIC_GLOBALS)")
     parser.add_option('--max-complexity', default=-1, action='store',
                       type='int', help="McCabe complexity treshold")
     parser.add_option('-v', '--verbose', default=0, action='count',
diff --git a/flake8/run.py b/flake8/run.py
index 4a7ddfa..8683e50 100644
--- a/flake8/run.py
+++ b/flake8/run.py
@@ -47,14 +47,18 @@ def _get_python_files(paths):
 def main():
     options, args = pep8.process_options()
     complexity = options.max_complexity
+    builtins = set(options.builtins)
     warnings = 0
+
+    if builtins:
+        orig_builtins = set(pyflakes._MAGIC_GLOBALS)
+        pyflakes._MAGIC_GLOBALS = orig_builtins | builtins
     if args:
         for path in _get_python_files(args):
             warnings += check_file(path, complexity)
     else:
         stdin = sys.stdin.read()
         warnings += check_code(stdin, complexity)
-
     raise SystemExit(warnings > 0)