diff --git a/src/aprsis2.proto b/src/aprsis2.proto
index 0b3bc7d..b3eb9eb 100644
--- a/src/aprsis2.proto
+++ b/src/aprsis2.proto
@@ -1,3 +1,4 @@
+syntax = "proto2";
 
 //
 //	A server sends an IS2ServerSignature to all new clients.