diff --git a/src/base58.js b/src/base58.js
index c64683d..9313c55 100644
--- a/src/base58.js
+++ b/src/base58.js
@@ -1,6 +1,7 @@
 (function (Bitcoin) {
   Bitcoin.Base58 = {
     alphabet: "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz",
+    validRegex: /^[1-9A-HJ-NP-Za-km-z]+$/,
     base: BigInteger.valueOf(58),
 
     /**
@@ -45,6 +46,9 @@
       var leadingZerosNum = 0;
       for (var i = input.length - 1; i >= 0; i--) {
         var alphaIndex = B58.alphabet.indexOf(input[i]);
+        if (alphaIndex < 0) {
+          throw "Invalid character";
+        }	
         bi = bi.add(BigInteger.valueOf(alphaIndex)
                     .multiply(B58.base.pow(input.length - 1 -i)));