--- a/config/mozunit.py
+++ b/config/mozunit.py
@@ -180,28 +180,28 @@ class MockedOpen(object):
                 self._wrapped_isdir(p) or
                 self._orig_path_exists(p))
 
     def _wrapped_isfile(self, p):
         p = normcase(p)
         if p in self.files:
             return True
 
-        abspath = os.path.abspath(p)
+        abspath = normcase(os.path.abspath(p))
         if abspath in self.files:
             return True
 
         return self._orig_path_isfile(p)
 
     def _wrapped_isdir(self, p):
         p = normcase(p)
         p = p if p.endswith(('/', '\\')) else p + os.sep
         if any(f.startswith(p) for f in self.files):
             return True
 
-        abspath = os.path.abspath(p) + os.sep
+        abspath = normcase(os.path.abspath(p) + os.sep)
         if any(f.startswith(abspath) for f in self.files):
             return True
 
         return self._orig_path_exists(p)
 
 def main(*args, **kwargs):
     unittest.main(testRunner=MozTestRunner(), *args, **kwargs)