diff --git a/app/Actions/EnsureCostBasisAddedToSale.php b/app/Actions/EnsureCostBasisAddedToSale.php
index b0efbe2..8908654 100644
--- a/app/Actions/EnsureCostBasisAddedToSale.php
+++ b/app/Actions/EnsureCostBasisAddedToSale.php
@@ -14,12 +14,18 @@ class EnsureCostBasisAddedToSale
         // cost basis is required for sales to calculate realized gains
         if ($model->transaction_type == 'SELL') {
 
-            $average_cost_basis = Transaction::where([
+            $cost_basis = Transaction::where([
                 'portfolio_id' => $model->portfolio_id,
                 'symbol' => $model->symbol,
                 'transaction_type' => 'BUY',
             ])->whereDate('date', '<=', $model->date)
-                ->average('cost_basis');
+                ->selectRaw('SUM(transactions.cost_basis * transactions.quantity) as total_cost_basis')
+                ->selectRaw('SUM(transactions.quantity) as total_quantity')
+                ->first();
+
+            $average_cost_basis = empty($cost_basis->total_quantity)
+                ? 0
+                : $cost_basis->total_cost_basis / $cost_basis->total_quantity;
 
             $model->cost_basis = $average_cost_basis ?? 0;
         }