diff --git a/portnums.proto b/portnums.proto
index 6f37e3e..65fa52b 100644
--- a/portnums.proto
+++ b/portnums.proto
@@ -119,6 +119,13 @@ enum PortNum {
      */
      ENVIRONMENTAL_MEASUREMENT_APP = 67;
 
+    /*
+     * Experimental tools for estimating node position without a GPS
+     * Maintained by Github user a-f-G-U-C (a Meshtastic contributor)
+     * Project files at https://github.com/a-f-G-U-C/Meshtastic-ZPS
+     */
+    ZPS_APP = 68;
+
     /*
      * Private applications should use portnums >= 256.
      * To simplify initial development and testing you can use "PRIVATE_APP"