diff --git a/tab.py b/tab.py
index 33ddeb4..0d82c17 100644
--- a/tab.py
+++ b/tab.py
@@ -294,7 +294,9 @@ class StackTabber2(Tabber):
         else:
             return 0
     def _get_next_level(self):
-        return self._get_curr_level() + self.mode.tabwidth
+        curr = self._get_curr_level()
+        if curr is None: return None
+        return curr + self.mode.tabwidth
     def _save_curr_level(self):
         self.curr_level = self._get_curr_level()