diff --git a/src/actions/portfolio.ts b/src/actions/portfolio.ts
index c17ec11..0279a82 100644
--- a/src/actions/portfolio.ts
+++ b/src/actions/portfolio.ts
@@ -54,7 +54,7 @@ function calculateCnyValueFromPrice(
 
   const directRate = getRate(rateMap, baseCurrency, 'CNY');
   if (directRate) {
-    return quantity.times(price).times(directRate);
+    return quantity.times(price).times(new Big(directRate));
   }
 
   const usdToCny = getRate(rateMap, 'USD', 'CNY');
@@ -64,7 +64,7 @@ function calculateCnyValueFromPrice(
 
   const usdRate = getRate(rateMap, baseCurrency, 'USD');
   if (usdRate) {
-    return quantity.times(price).times(usdRate).times(usdToCny);
+    return quantity.times(price).times(new Big(usdRate)).times(new Big(usdToCny));
   }
 
   return new Big('0');
@@ -116,16 +116,16 @@ export async function getPortfolioPositions(): Promise<Position[]> {
     const holding = holdings.get(tx.assetId)!;
 
     if (tx.txType === 'BUY') {
-      holding.quantity = holding.quantity.plus(tx.quantity);
-      const costPerUnit = tx.quantity.times(tx.price);
-      const costCny = costPerUnit.times(tx.exchangeRate || '1');
+      holding.quantity = holding.quantity.plus(new Big(tx.quantity));
+      const costPerUnit = new Big(tx.quantity).times(new Big(tx.price));
+      const costCny = costPerUnit.times(new Big(tx.exchangeRate || '1'));
       holding.totalCostCny = holding.totalCostCny.plus(costCny);
     } else if (tx.txType === 'SELL') {
-      holding.quantity = holding.quantity.minus(tx.quantity);
+      holding.quantity = holding.quantity.minus(new Big(tx.quantity));
     } else if (tx.txType === 'AIRDROP') {
-      holding.quantity = holding.quantity.plus(tx.quantity);
+      holding.quantity = holding.quantity.plus(new Big(tx.quantity));
     } else if (tx.txType === 'DIVIDEND') {
-      holding.quantity = holding.quantity.plus(tx.quantity);
+      holding.quantity = holding.quantity.plus(new Big(tx.quantity));
     }
 
     if (tx.assetLatestPrice) {