diff --git a/flake8/plugins/pyflakes.py b/flake8/plugins/pyflakes.py
index 85465fc..d787344 100644
--- a/flake8/plugins/pyflakes.py
+++ b/flake8/plugins/pyflakes.py
@@ -97,7 +97,7 @@ class FlakesChecker(pyflakes.checker.Checker):
     def parse_options(cls, options):
         """Parse option values from Flake8's OptionManager."""
         if options.builtins:
-            cls.builtIns = cls.builtIns.union(options.builtins.split(','))
+            cls.builtIns = cls.builtIns.union(options.builtins)
         cls.withDoctest = options.doctests
 
         included_files = []