diff --git a/index.js b/index.js
index cf762b5..80542fd 100644
--- a/index.js
+++ b/index.js
@@ -51,10 +51,15 @@ function MLLPServer(host, port, logger) {
             var header = [data[0]];
 
             //switch around sender/receiver names
-            header[0][3] = data[0][5];
-            header[0][4] = data[0][6];
-            header[0][5] = data[0][3];
-            header[0][6] = data[0][4];
+            var receiverApp = data[0][5];
+            var receiverInst = data[0][6];
+            var senderApp = data[0][3];
+            var senderInst = data[0][4];
+
+            header[0][3] = receiverApp;
+            header[0][4] = receiverInst;
+            header[0][5] = senderApp;
+            header[0][6] = senderInst;
 
             var result = hl7.serializeJSON(header);
             result = result + "\r" + "MSA|" + ack_type + "|" + msg_id;