diff --git a/.appveyor.yml b/.appveyor.yml
index 4a1d13c..ab4b7e2 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -5,4 +5,4 @@ install:
 build: off
 
 test_script:
-  - python -m tox
+  - python -m tox -e py27,py33,py34,py35
diff --git a/src/flake8/utils.py b/src/flake8/utils.py
index f432dac..1e1eaa0 100644
--- a/src/flake8/utils.py
+++ b/src/flake8/utils.py
@@ -59,7 +59,8 @@ def normalize_path(path, parent=os.curdir):
     separator = os.path.sep
     # NOTE(sigmavirus24): os.path.altsep may be None
     alternate_separator = os.path.altsep or ''
-    if separator in path or alternate_separator in path:
+    if separator in path or (alternate_separator and
+                             alternate_separator in path):
         path = os.path.abspath(os.path.join(parent, path))
     return path.rstrip(separator + alternate_separator)