diff --git a/async/index.browser.js b/async/index.browser.js
index 68362643..2ead6973 100644
--- a/async/index.browser.js
+++ b/async/index.browser.js
@@ -4,39 +4,38 @@
 var crypto = self.crypto || self.msCrypto
 
 // This alphabet uses a-z A-Z 0-9 _- symbols.
-// Despite the fact the source code is quite long, its entropy
-// is low and there are lots of duplicates - just what compressors
-// like GZIP and Brotli likes the best.
-var i
-var url = '_-' + String.fromCharCode(
-  // ASCII codes for 0...9
-  i = 48, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
+// Symbols are generated for better gzip compression.
+// Final url is
+// '-_zyxwvutsrqponmlkjihgfedcba9876543210ZYXWVUTSRQPONMLKJIHGFEDCBA'
+var url = '-_'
 
-  // ASCII codes for A...Z
-  i += 8, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
+var i = 36
+while (i--) {
+  // 36 is radix.
+  // Number.prototype.toString(36) returns number in Base36 representation.
+  // Base36 is like hex,
+  // but Base36 is represented using the numerals 0–9 and the Latin letters a-z
+  url += i.toString(36)
+}
 
-  // ASCII codes for a...z
-  i += 7, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1
-)
+i = 36
+// Loop from 36 to 10 (from Z to A in Base36)
+while (i-- - 10) {
+  url += i.toString(36).toUpperCase()
+}
 
 module.exports = function (size) {
-  size = size || 21
   var id = ''
-  var bytes = crypto.getRandomValues(new Uint8Array(size))
+  var bytes = crypto.getRandomValues(new Uint8Array(size || 21))
+  i = size || 21
+
   // Compact alternative for `for (var i = 0; i < size; i++)`
-  while (size--) {
+  while (i--) {
     // We can’t use bytes bigger than the alphabet. 63 is 00111111 bitmask.
     // This mask reduces random byte 0-255 to 0-63 values.
     // There is no need in `|| ''` and `* 1.6` hacks in here,
     // because bitmask trim bytes exact to alphabet size.
-    id += url[bytes[size] & 63]
+    id += url[bytes[i] & 63]
   }
   return Promise.resolve(id)
 }
diff --git a/index.browser.js b/index.browser.js
index ea4e395f..2f5e2f65 100644
--- a/index.browser.js
+++ b/index.browser.js
@@ -21,39 +21,38 @@ if (process.env.NODE_ENV !== 'production') {
 var crypto = self.crypto || self.msCrypto
 
 // This alphabet uses a-z A-Z 0-9 _- symbols.
-// Despite the fact the source code is quite long, its entropy
-// is low and there are lots of duplicates - just what compressors
-// like GZIP and Brotli likes the best.
-var i
-var url = '_-' + String.fromCharCode(
-  // ASCII codes for 0...9
-  i = 48, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
+// Symbols are generated for better gzip compression.
+// Final url is
+// '-_zyxwvutsrqponmlkjihgfedcba9876543210ZYXWVUTSRQPONMLKJIHGFEDCBA'
+var url = '-_'
 
-  // ASCII codes for A...Z
-  i += 8, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
+var i = 36
+while (i--) {
+  // 36 is radix.
+  // Number.prototype.toString(36) returns number in Base36 representation.
+  // Base36 is like hex,
+  // but Base36 is represented using the numerals 0–9 and the Latin letters a-z
+  url += i.toString(36)
+}
 
-  // ASCII codes for a...z
-  i += 7, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1
-)
+i = 36
+// Loop from 36 to 10 (from Z to A in Base36)
+while (i-- - 10) {
+  url += i.toString(36).toUpperCase()
+}
 
 module.exports = function (size) {
-  size = size || 21
   var id = ''
-  var bytes = crypto.getRandomValues(new Uint8Array(size))
+  var bytes = crypto.getRandomValues(new Uint8Array(size || 21))
+  i = size || 21
+
   // Compact alternative for `for (var i = 0; i < size; i++)`
-  while (size--) {
+  while (i--) {
     // We can’t use bytes bigger than the alphabet. 63 is 00111111 bitmask.
     // This mask reduces random byte 0-255 to 0-63 values.
     // There is no need in `|| ''` and `* 1.6` hacks in here,
     // because bitmask trim bytes exact to alphabet size.
-    id += url[bytes[size] & 63]
+    id += url[bytes[i] & 63]
   }
   return id
 }
diff --git a/non-secure/index.js b/non-secure/index.js
index 08c4e319..94f0cbd9 100644
--- a/non-secure/index.js
+++ b/non-secure/index.js
@@ -1,25 +1,23 @@
 // This alphabet uses a-z A-Z 0-9 _- symbols.
-// Despite the fact the source code is quite long, its entropy
-// is low and there are lots of duplicates - just what compressors
-// like GZIP and Brotli likes the best.
-var i
-var url = '_-' + String.fromCharCode(
-  // ASCII codes for 0...9
-  i = 48, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
+// Symbols are generated for better gzip compression.
+// Final url is
+// '-_zyxwvutsrqponmlkjihgfedcba9876543210ZYXWVUTSRQPONMLKJIHGFEDCBA'
+var url = '-_'
 
-  // ASCII codes for A...Z
-  i += 8, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
+var i = 36
+while (i--) {
+  // 36 is radix.
+  // Number.prototype.toString(36) returns number in Base36 representation.
+  // Base36 is like hex,
+  // but Base36 is represented using the numerals 0–9 and the Latin letters a-z
+  url += i.toString(36)
+}
 
-  // ASCII codes for a...z
-  i += 7, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1
-)
+i = 36
+// Loop from 36 to 10 (from Z to A in Base36)
+while (i-- - 10) {
+  url += i.toString(36).toUpperCase()
+}
 
 /**
  * Generate URL-friendly unique ID. This method use non-secure predictable
@@ -37,10 +35,10 @@ var url = '_-' + String.fromCharCode(
  * @function
  */
 module.exports = function (size) {
-  size = size || 21
   var id = ''
+  i = size || 21
   // Compact alternative for `for (var i = 0; i < size; i++)`
-  while (size--) {
+  while (i--) {
     // `| 0` is compact and faster alternative for `Math.floor()`
     id += url[Math.random() * 64 | 0]
   }
diff --git a/package.json b/package.json
index c90d26e9..2e3f8619 100644
--- a/package.json
+++ b/package.json
@@ -66,7 +66,7 @@
   "size-limit": [
     {
       "path": "index.js",
-      "limit": "127 B"
+      "limit": "119 B"
     },
     {
       "path": "generate.js",
@@ -78,7 +78,7 @@
     },
     {
       "path": "non-secure/index.js",
-      "limit": "89 B"
+      "limit": "82 B"
     },
     {
       "path": "non-secure/generate.js",
@@ -86,7 +86,7 @@
     },
     {
       "path": "async/index.js",
-      "limit": "139 B"
+      "limit": "130 B"
     },
     {
       "path": "async/generate.js",
diff --git a/url.js b/url.js
index 5be82d1c..cf95ea4d 100644
--- a/url.js
+++ b/url.js
@@ -3,8 +3,6 @@
 // is low and there are lots of duplicates - just what compressors
 // like GZIP and Brotli likes the best.
 
-var i
-
 /**
  * URL safe symbols.
  *
@@ -15,20 +13,14 @@ var i
  * const url = require('nanoid/url')
  * generate(url, 10) //=> "Uakgb_J5m9"
  */
-module.exports = '_-' + String.fromCharCode(
-  // ASCII codes for 0...9
-  i = 48, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
-
-  // ASCII codes for A...Z
-  i += 8, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1,
 
-  // ASCII codes for a...z
-  i += 7, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1, i += 1,
-  i += 1, i += 1
-)
+module.exports = '-_'
+var i = 36
+while (i--) {
+  // 36 is radix.
+  // Number.prototype.toString(36) returns number in Base36 representation.
+  // Base36 is like hex,
+  // but Base36 is represented using the numerals 0–9 and the Latin letters a-z
+  module.exports += i.toString(36)
+  i > 9 && (module.exports += i.toString(36).toUpperCase())
+}