diff --git a/lib/TransactionBuilder.js b/lib/TransactionBuilder.js
index 8c03baa..df5d02c 100644
--- a/lib/TransactionBuilder.js
+++ b/lib/TransactionBuilder.js
@@ -201,7 +201,7 @@ TransactionBuilder.prototype._setInputMap = function() {
     var scriptType = scriptPubKey.classify();
 
     if (scriptType === Script.TX_UNKNOWN)
-      throw new Error('unkown output type at:' + i +
+      throw new Error('Unknown script pubkey type at:' + i +
         ' Type:' + scriptPubKey.getRawOutType());
 
     inputMap.push({