diff --git a/apptools/persistence/file_path.py b/apptools/persistence/file_path.py
index 71932b2d4..69227b537 100644
--- a/apptools/persistence/file_path.py
+++ b/apptools/persistence/file_path.py
@@ -67,7 +67,7 @@ def set_relative(self, base_f_name):
         ret = (_src.count(os.sep) * ('..' + os.sep)) + _dst
 
         # Make it posix style.
-        if os.sep is not '/':
+        if os.sep != '/':
             ret.replace(os.sep, '/')
 
         # Store it.