diff --git a/src/sakia/core/money/quantitative.py b/src/sakia/core/money/quantitative.py
index 55434344501b59050c7c50bb9d1ac83297f67561..e2726565ba42942971a58c0c334db34a53c36b90 100644
--- a/src/sakia/core/money/quantitative.py
+++ b/src/sakia/core/money/quantitative.py
@@ -37,7 +37,7 @@ class Quantitative(BaseReferential):
 
     @property
     def diff_units(self):
-        return Quantitative.units
+        return self.units
 
     async def value(self):
         """