diff --git a/index.js b/index.js
index 3cf497d..6bf84b3 100644
--- a/index.js
+++ b/index.js
@@ -1,11 +1,30 @@
-var RFC4648 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'
-var RFC4648_HEX = '0123456789ABCDEFGHIJKLMNOPQRSTUV'
-var CROCKFORD = '0123456789ABCDEFGHJKMNPQRSTVWXYZ'
+function createAlphabet (str) {
+  var lookup = {}
+  for (var i = 0; i < str.length; i++) {
+    lookup[str.charAt(i)] = i
+  }
+  return lookup
+}
+
+var RFC4648 = createAlphabet('ABCDEFGHIJKLMNOPQRSTUVWXYZ234567')
+var RFC4648_HEX = createAlphabet('0123456789ABCDEFGHIJKLMNOPQRSTUV')
+var CROCKFORD = Object.assign(
+  createAlphabet('0123456789ABCDEFGHJKMNPQRSTVWXYZ'),
+  createAlphabet('0123456789ABCDEFGHJKMNPQRSTVWXYZ'.toLowerCase()),
+  {
+    'o': 0,
+    'O': 0,
+    'i': 1,
+    'I': 1,
+    'l': 1,
+    'L': 1
+  }
+)
 
 function readChar (alphabet, char) {
-  var idx = alphabet.indexOf(char)
+  var idx = alphabet[char]
 
-  if (idx === -1) {
+  if (idx === undefined) {
     throw new Error('Invalid character found: ' + char)
   }
 
@@ -27,7 +46,7 @@ module.exports = function base32Decode (input, variant) {
       break
     case 'Crockford':
       alphabet = CROCKFORD
-      input = input.toUpperCase().replace(/O/g, '0').replace(/[IL]/g, '1')
+      input = input.replace(/-+|([*~$=u]$)/ig, '')
       break
     default:
       throw new Error('Unknown base32 variant: ' + variant)
diff --git a/test.js b/test.js
index 97eae9c..29b4fa0 100644
--- a/test.js
+++ b/test.js
@@ -64,13 +64,27 @@ var testCases = [
   ['Crockford', '61', 'c4'],
   ['Crockford', '74657374', 'EHJQ6X0'],
   ['Crockford', '74657374', 'EHJQ6XO'],
+  ['Crockford', '74657374', 'ehjq6xo'],
   ['Crockford', '6c696e7573', 'DHMPWXBK'],
   ['Crockford', '6c696e7573', 'DhmPWXbK'],
   ['Crockford', '666f6f626172', 'CSQPYRK1E8'],
   ['Crockford', '666f6f626172', 'CSQPYRKLE8'],
-  ['Crockford', '666f6f626172', 'CSQPYRKIE8']
+  ['Crockford', '666f6f626172', 'CSQPYRKIE8'],
+  ['Crockford', '666f6f626172', 'csqpyrk1e8'],
+  ['Crockford', '666f6f626172', 'csqpyrkle8'],
+  ['Crockford', '666f6f626172', 'csqpyrkie8'],
+  ['Crockford', '666f6f626172', 'csq-pyr---kle8--'],
+  ['Crockford', '666f6f626172', 'csqpyrkie8*'],
+  ['Crockford', '666f6f626172', 'csqpyrkie8~'],
+  ['Crockford', '666f6f626172', 'csqpyrkie8$'],
+  ['Crockford', '666f6f626172', 'csqpyrkie8='],
+  ['Crockford', '666f6f626172', 'csqpyrkie8u'],
+  ['Crockford', '666f6f626172', 'csqpyrkie8U']
 ]
 
 testCases.forEach(function (testCase) {
   assert(isEqual(base32Decode(testCase[2], testCase[0]), hexToArrayBuffer(testCase[1])))
 })
+
+assert.throws(function () { base32Decode('&', 'RFC4648-HEX') })
+assert.throws(function () { base32Decode('&', 'Crockford') })