diff --git a/package.json b/package.json
index dff66fb5..9a7aadd3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "@balancer-labs/sor",
-    "version": "4.0.1-beta.7",
+    "version": "4.0.1-beta.8",
     "license": "GPL-3.0-only",
     "main": "dist/index.js",
     "module": "dist/index.esm.js",
diff --git a/src/pools/weightedPool/weightedMath.ts b/src/pools/weightedPool/weightedMath.ts
index 4a7f0e1c..142683a1 100644
--- a/src/pools/weightedPool/weightedMath.ts
+++ b/src/pools/weightedPool/weightedMath.ts
@@ -583,7 +583,7 @@ export function _spotPriceAfterSwapExactBPTInForTokenOut(
     );
     const wo = parseFloat(formatFixed(poolPairData.weightOut, 18));
     const Aibpt = amount.toNumber();
-    const f = parseFloat(formatFixed(poolPairData.swapFee.toNumber()));
+    const f = parseFloat(formatFixed(poolPairData.swapFee));
     return bnum(
         ((1 - Aibpt / Bbpt) ** ((-1 + wo) / wo) *
             Bbpt *