diff --git a/index.browser.js b/index.browser.js
index 8b51358c..9ec0a948 100644
--- a/index.browser.js
+++ b/index.browser.js
@@ -13,7 +13,7 @@ export let customRandom = (alphabet, defaultSize, getRandom) => {
   // `2^31 - 1` number, which exceeds the alphabet size.
   // For example, the bitmask for the alphabet size 30 is 31 (00011111).
   // `Math.clz32` is not used, because it is not available in browsers.
-  let mask = (2 << (Math.log(alphabet.length - 1) / Math.LN2)) - 1
+  let mask = (2 << Math.log2(alphabet.length - 1)) - 1
   // Though, the bitmask solution is not perfect since the bytes exceeding
   // the alphabet size are refused. Therefore, to reliably generate the ID,
   // the random bytes redundancy has to be satisfied.