diff --git a/widgetlib/inventory.py b/widgetlib/inventory.py
index 2a527d1..bfc959f 100644
--- a/widgetlib/inventory.py
+++ b/widgetlib/inventory.py
@@ -25,4 +25,4 @@ class Inventory:
 
     def total_value(self) -> float:
         """Return the total monetary value of all stock (Σ quantity × unit_price)."""
-        return float(sum(self._quantities.values()))
+        return sum(quantity * self._prices[sku] for sku, quantity in self._quantities.items())
