diff --git a/async/index.js b/async/index.js
index 72ee79b4..db04d9c0 100644
--- a/async/index.js
+++ b/async/index.js
@@ -1,4 +1,4 @@
-let { urlAlphabet } = require('..')
+let { urlAlphabet } = require('../url-alphabet')
 let { random } = require('./random')
 
 let customAlphabet = (alphabet, size) => {
diff --git a/index.browser.js b/index.browser.js
index e9a45130..e9233f90 100644
--- a/index.browser.js
+++ b/index.browser.js
@@ -1,6 +1,8 @@
 // This file replaces `index.js` in bundlers like webpack or Rollup,
 // according to `browser` config in `package.json`.
 
+let { urlAlphabet } = require('./url-alphabet')
+
 if (process.env.NODE_ENV !== 'production') {
   // All bundlers will remove this block in the production bundle.
   if (
@@ -28,11 +30,6 @@ if (process.env.NODE_ENV !== 'production') {
   }
 }
 
-// This alphabet uses `A-Za-z0-9_-` symbols. The genetic algorithm helped
-// optimize the gzip compression for this alphabet.
-let urlAlphabet =
-  'ModuleSymbhasOwnPr-0123456789ABCDEFGHNRVfgctiUvz_KqYTJkLxpZXIjQW'
-
 let random = bytes => crypto.getRandomValues(new Uint8Array(bytes))
 
 let customRandom = (alphabet, size, getRandom) => {
diff --git a/index.js b/index.js
index 057794fd..5d8165a2 100644
--- a/index.js
+++ b/index.js
@@ -1,7 +1,6 @@
 let crypto = require('crypto')
 
-let urlAlphabet =
-  '_-0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
+let { urlAlphabet } = require('./url-alphabet')
 
 // We reuse buffers with the same size to avoid memory fragmentations
 // for better performance.
diff --git a/url-alphabet/index.js b/url-alphabet/index.js
new file mode 100644
index 00000000..8c9d70d8
--- /dev/null
+++ b/url-alphabet/index.js
@@ -0,0 +1,6 @@
+// This alphabet uses `A-Za-z0-9_-` symbols. The genetic algorithm helped
+// optimize the gzip compression for this alphabet.
+let urlAlphabet =
+  'ModuleSymbhasOwnPr-0123456789ABCDEFGHNRVfgctiUvz_KqYTJkLxpZXIjQW'
+
+module.exports = { urlAlphabet }