diff --git a/mypy/sitepkgs.py b/mypy/sitepkgs.py
index 382fab8d8bc9..2a13e4b246bf 100644
--- a/mypy/sitepkgs.py
+++ b/mypy/sitepkgs.py
@@ -7,10 +7,13 @@
 possible.
 """
 
-import sys
-sys.path = sys.path[1:]  # we don't want to pick up mypy.types
+if __name__ == '__main__':
+    import sys
+    sys.path = sys.path[1:]  # we don't want to pick up mypy.types
+
 from distutils.sysconfig import get_python_lib
 import site
+
 MYPY = False
 if MYPY:
     from typing import List