diff --git a/xmlout.js b/xmlout.js
index 2b2ce9d..f09aed1 100644
--- a/xmlout.js
+++ b/xmlout.js
@@ -176,7 +176,11 @@ function prefixMessageWithSN(data) {
 
     sn = '';
 
-    if (data['MESSAGE'].search(/^SN=.+;/) == -1) {
+    if (data.SN && data.SN.trim()) {
+        sn = data['SN'].replace(/ /g, '-').replace(/-*/g, '-').trim();
+        return 'SN=' + sn + '; ' + data['MESSAGE'];
+    }
+    else if (data['MESSAGE'].search(/^SN=.+;/) == -1) {
         if (data['SN'] && data['SN'].trim()) {
             sn = data['SN'].trim();
         }