diff --git a/benchmark/buffers/buffer-base64-decode.js b/benchmark/buffers/buffer-base64-decode.js
index 0ac694fe8c4ae7..d05b9ab3787fce 100644
--- a/benchmark/buffers/buffer-base64-decode.js
+++ b/benchmark/buffers/buffer-base64-decode.js
@@ -9,11 +9,12 @@ const bench = common.createBenchmark(main, {
 
 function main({ n, size }) {
   const s = 'abcd'.repeat(size);
+  const encodedSize = s.length * 3 / 4;
   // eslint-disable-next-line node-core/no-unescaped-regexp-dot
   s.match(/./);  // Flatten string.
   assert.strictEqual(s.length % 4, 0);
-  const b = Buffer.allocUnsafe(s.length / 4 * 3);
-  b.write(s, 0, s.length, 'base64');
+  const b = Buffer.allocUnsafe(encodedSize);
+  b.write(s, 0, encodedSize, 'base64');
   bench.start();
   for (var i = 0; i < n; i += 1) b.base64Write(s, 0, s.length);
   bench.end(n);