diff --git a/lib/serializer.js b/lib/serializer.js
index 24917433..1a006d5f 100644
--- a/lib/serializer.js
+++ b/lib/serializer.js
@@ -41,7 +41,7 @@ module.exports = class Serializer {
 
   asNumber (i) {
     // fast cast to number
-    const num = +i
+    const num = Number(i)
     // check if number is NaN
     // eslint-disable-next-line no-self-compare
     if (num !== num) {
diff --git a/test/asNumber.test.js b/test/asNumber.test.js
new file mode 100644
index 00000000..5e68b922
--- /dev/null
+++ b/test/asNumber.test.js
@@ -0,0 +1,13 @@
+'use strict'
+
+const test = require('tap').test
+
+test('asNumber should convert BigInt', (t) => {
+  t.plan(1)
+  const Serializer = require('../lib/serializer')
+  const serializer = new Serializer()
+
+  const number = serializer.asNumber(11753021440n)
+
+  t.equal(number, '11753021440')
+})