diff --git a/mixin.py b/mixin.py
index 1ffdd6f..dc235ac 100644
--- a/mixin.py
+++ b/mixin.py
@@ -168,6 +168,9 @@ class EdocumentMixin(object):
         Args:
             line (record): model account.invoice.line
         """
+        if not hasattr(line, 'modegross'):
+            return line.amount
+
         if line.modegross == 'net':
             return line.amount
         elif line.modegross == 'gross':