diff --git a/tiramisu/storage/dictionary/setting.py b/tiramisu/storage/dictionary/setting.py
index bfa00ff..ede22ee 100644
--- a/tiramisu/storage/dictionary/setting.py
+++ b/tiramisu/storage/dictionary/setting.py
@@ -62,7 +62,11 @@ class Permissives(Cache):
         super(Permissives, self).__init__(storage)
 
     def setpermissive(self, path, permissive):
-        self._permissives[path] = frozenset(permissive)
+        if not permissive:
+            if path in self._permissives:
+                del self._permissives[path]
+        else:
+            self._permissives[path] = permissive
 
     def getpermissive(self, path=None):
         return self._permissives.get(path, frozenset())