diff --git a/lib/session.js b/lib/session.js
index 8474a89..a367df1 100644
--- a/lib/session.js
+++ b/lib/session.js
@@ -378,7 +378,7 @@ function longSms(pduObj) {
 	                                                                              // 4th octet and length is
 	                                                                              // header size -2 octets
 	    partsCount    = pduObj.params.short_message[2 + csmsReference.length + 1],
-	    partNr        = pduObj.params.short_message[2 + csmsReference.length + 1],
+	    partNr        = pduObj.params.short_message[2 + csmsReference.length + 2],
 	    longSmsId     = pduObj.params.source_addr + '_' + pduObj.params.destination_addr + '_' + csmsReference;
 
 	if (this.longSmses[longSmsId] === undefined) {