diff --git a/README.md b/README.md
index bd3af4d..50b3b54 100644
--- a/README.md
+++ b/README.md
@@ -40,6 +40,7 @@ yarn add string-natural-compare
 + `strB` (_string_)
 + `options` (_object_) - Optional options object with the following options:
   + `caseInsensitive` (_boolean_) - Set to `true` to compare strings case-insensitively. Default: `false`.
+  + `alphabet` (_string_) - A string of characters that define a custom character ordering. Default: `undefined`.
 
 ```js
 const naturalCompare = require('string-natural-compare');
@@ -83,9 +84,9 @@ hotelRooms.sort((a, b) => (
 
 
 // When text transformation is needed or when doing a case-insensitive sort on a
-// large array, it is best for performance to pre-compute the transformed text
-// and store it in that object. This way, the text transformation will not be
-// needed for every comparison while sorting.
+// large array of objects, it is best for performance to pre-compute the
+// transformed text and store it on the object. This way, the text will not need
+// to be transformed for every comparison while sorting.
 const cars = [
   {make: 'Audi', model: 'R8'},
   {make: 'Porsche', model: '911 Turbo S'}
@@ -95,23 +96,13 @@ for (const car of cars) {
   car.sortKey = (car.make + ' ' + car.model).toLowerCase();
 }
 cars.sort((a, b) => naturalCompare(a.sortKey, b.sortKey));
-```
-
-### Custom Alphabet
-
-It is possible to configure a custom alphabet to achieve a desired character ordering.
-
-```js
-const naturalCompare = require('string-natural-compare');
 
-// Estonian alphabet
-naturalCompare.alphabet = 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy';
-['t', 'z', 'x', 'õ'].sort(naturalCompare);
-// -> ['z', 't', 'õ', 'x']
 
-// Russian alphabet
-naturalCompare.alphabet = 'АБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдеёжзийклмнопрстуфхцчшщъыьэюя';
-['Ё', 'А', 'б', 'Б'].sort(naturalCompare);
+// Using a custom alphabet (Russian alphabet)
+const russianOpts = {
+  alphabet: 'АБВГДЕЁЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯабвгдеёжзийклмнопрстуфхцчшщъыьэюя',
+};
+['Ё', 'А', 'б', 'Б'].sort((a, b) => naturalCompare(a, b, russianOpts));
 // -> ['А', 'Б', 'Ё', 'б']
 ```
 
diff --git a/benchmark/run.js b/benchmark/run.js
index d2b8793..dbc3025 100644
--- a/benchmark/run.js
+++ b/benchmark/run.js
@@ -104,32 +104,32 @@ if (suite.length) {
     .run();
 }
 
-naturalCompareMaster.alphabet = 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy';
-naturalCompareLocal.alphabet = 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy';
-
 const alphabetSuite = new Benchmark.Suite();
+const opts = {
+  alphabet: 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy',
+};
 
 if (config.has('6')) {
   alphabetSuite
     .add('6) custom alphabet included characters master', () => {
-      naturalCompareMaster('š.txt', 'z.txt');
-      naturalCompareMaster('z.txt', 'š.txt');
+      naturalCompareMaster('š.txt', 'z.txt', opts);
+      naturalCompareMaster('z.txt', 'š.txt', opts);
     })
     .add('6) custom alphabet included characters local', () => {
-      naturalCompareLocal('š.txt', 'z.txt');
-      naturalCompareLocal('z.txt', 'š.txt');
+      naturalCompareLocal('š.txt', 'z.txt', opts);
+      naturalCompareLocal('z.txt', 'š.txt', opts);
     });
 }
 
 if (config.has('7')) {
   alphabetSuite
     .add('7) custom alphabet missing characters master', () => {
-      naturalCompareMaster('é.txt', 'à.txt');
-      naturalCompareMaster('à.txt', 'é.txt');
+      naturalCompareMaster('é.txt', 'à.txt', opts);
+      naturalCompareMaster('à.txt', 'é.txt', opts);
     })
     .add('7) custom alphabet missing characters local', () => {
-      naturalCompareLocal('é.txt', 'à.txt');
-      naturalCompareLocal('à.txt', 'é.txt');
+      naturalCompareLocal('é.txt', 'à.txt', opts);
+      naturalCompareLocal('à.txt', 'é.txt', opts);
     });
 }
 
diff --git a/natural-compare.js b/natural-compare.js
index 860b191..96688a8 100644
--- a/natural-compare.js
+++ b/natural-compare.js
@@ -1,7 +1,6 @@
 'use strict';
 
-var alphabet;
-var alphabetIndexMap = [];
+const defaultAlphabetIndexMap = [];
 
 function isNumberCode(code) {
   return code >= 48 && code <= 57;
@@ -15,16 +14,23 @@ function naturalCompare(a, b, opts) {
     throw new TypeError(`The second argument must be a string. Received type '${typeof b}'`);
   }
 
-  if (opts && opts.caseInsensitive) {
-    a = a.toLowerCase();
-    b = b.toLowerCase();
-  }
-
+  var alphabetIndexMap = defaultAlphabetIndexMap;
   var lengthA = a.length;
   var lengthB = b.length;
   var aIndex = 0;
   var bIndex = 0;
 
+  if (opts) {
+    if (opts.caseInsensitive) {
+      a = a.toLowerCase();
+      b = b.toLowerCase();
+    }
+
+    if (opts.alphabet) {
+      alphabetIndexMap = buildAlphabetIndexMap(opts.alphabet);
+    }
+  }
+
   while (aIndex < lengthA && bIndex < lengthB) {
     var charCodeA = a.charCodeAt(aIndex);
     var charCodeB = b.charCodeAt(bIndex);
@@ -99,33 +105,30 @@ function naturalCompare(a, b, opts) {
   return lengthA - lengthB;
 }
 
-Object.defineProperties(naturalCompare, {
-  alphabet: {
-    get() {
-      return alphabet;
-    },
+const alphabetIndexMapCache = {};
 
-    set(value) {
-      alphabet = value;
-      alphabetIndexMap = [];
+function buildAlphabetIndexMap(alphabet) {
+  const existingMap = alphabetIndexMapCache[alphabet];
+  if (existingMap !== undefined) {
+    return existingMap;
+  }
 
-      if (!alphabet) {
-        return;
-      }
+  const indexMap = [];
+  const maxCharCode = alphabet.split('').reduce((maxCode, char) => {
+    return Math.max(maxCode, char.charCodeAt(0));
+  }, 0);
 
-      const maxCharCode = alphabet.split('').reduce((maxCode, char) => {
-        return Math.max(maxCode, char.charCodeAt(0));
-      }, 0);
+  for (let i = 0; i <= maxCharCode; i++) {
+    indexMap.push(-1);
+  }
 
-      for (let i = 0; i <= maxCharCode; i++) {
-        alphabetIndexMap.push(-1);
-      }
+  for (let i = 0; i < alphabet.length; i++) {
+    indexMap[alphabet.charCodeAt(i)] = i;
+  }
 
-      for (let i = 0; i < alphabet.length; i++) {
-        alphabetIndexMap[alphabet.charCodeAt(i)] = i;
-      }
-    },
-  },
-});
+  alphabetIndexMapCache[alphabet] = indexMap;
+
+  return indexMap;
+}
 
 module.exports = naturalCompare;
diff --git a/test/test.js b/test/test.js
index 0f2fc8f..68b801a 100644
--- a/test/test.js
+++ b/test/test.js
@@ -245,10 +245,12 @@ describe('naturalCompare()', () => {
   });
 
   it('should compare strings using the provided alphabet', () => {
-    naturalCompare.alphabet = 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy';
+    const opts = {
+      alphabet: 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy',
+    };
 
     ['Д', 'a', 'ä', 'B', 'Š', 'X', 'A', 'õ', 'u', 'z', '1', '2', '9', '10']
-      .sort(naturalCompare)
+      .sort((a, b) => naturalCompare(a, b, opts))
       .should.deepEqual(['1', '2', '9', '10', 'A', 'B', 'Š', 'X', 'a', 'z', 'u', 'õ', 'ä', 'Д']);
 
     naturalCompare.alphabet = null; // Reset alphabet for other tests
@@ -267,27 +269,16 @@ describe('naturalCompare()', () => {
     });
 
     it('should compare strings using the provided alphabet', () => {
-      naturalCompare.alphabet = 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy';
+      const opts = {
+        alphabet: 'ABDEFGHIJKLMNOPRSŠZŽTUVÕÄÖÜXYabdefghijklmnoprsšzžtuvõäöüxy',
+        caseInsensitive: true,
+      };
 
       ['Д', 'a', 'ä', 'B', 'Š', 'X', 'Ü', 'õ', 'u', 'z', '1', '2', '9', '10']
-        .sort((a, b) => naturalCompare(a, b, {caseInsensitive: true}))
+        .sort((a, b) => naturalCompare(a, b, opts))
         .should.deepEqual(['1', '2', '9', '10', 'a', 'B', 'Š', 'z', 'u', 'õ', 'ä', 'Ü', 'X', 'Д']);
     });
 
   });
 
 });
-
-
-describe('naturalCompare.alphabet', () => {
-
-  it('can be set and retrieved', () => {
-    naturalCompare.alphabet = 'cba';
-    naturalCompare.alphabet.should.equal('cba');
-  });
-
-  it('can be set to null', () => {
-    naturalCompare.alphabet = null;
-  });
-
-});