diff --git a/mode/python.py b/mode/python.py
index 523b422..9be9f34 100644
--- a/mode/python.py
+++ b/mode/python.py
@@ -79,6 +79,7 @@ class PythonTabber(tab2.StackTabber):
     def _calc_level(self, y):
         # ok, so first remember where we are going, and find our starting point
         target = y
+        y = max(0, y - 1)
         while not self.is_base(y) and y > 0:
             y -= 1