diff --git a/lib/sepa.js b/lib/sepa.ts
similarity index 99%
rename from lib/sepa.js
rename to lib/sepa.ts
index a2ebc94..b095618 100644
--- a/lib/sepa.js
+++ b/lib/sepa.ts
@@ -62,8 +62,9 @@
   }
 
   function getPainXMLVersion(painFormat) {
+    // 008 is the version by default.
     var inc = painFormat.indexOf('pain.008') === 0 ?  1 : 0;
-    return parseInt(painFormat.substr(-2), 10) + inc;
+    return parseInt(painFormat.substr(2), 10) + inc;
   }
 
   function SepaDocument(painFormat, options) {