diff --git a/linopy/expressions.py b/linopy/expressions.py
index 197482ad..e0414483 100644
--- a/linopy/expressions.py
+++ b/linopy/expressions.py
@@ -1275,7 +1275,9 @@ def _add_constant_legacy(
             if is_nan_scalar(other):
                 check_user_nan()
             warn_legacy_absence(self.const)
-            return self.assign(const=self.const.fillna(0) + other)
+            return self.assign(
+                const=self.const.fillna(0) + cast("float | np.number", other)
+            )
         self_const, da, needs_reindex = self._broadcast_and_align(
             other, fill_value, join
         )