diff --git a/src/processor/proto/process_state.proto b/src/processor/proto/process_state.proto
index 8d871a5d..5ff6194c 100644
--- a/src/processor/proto/process_state.proto
+++ b/src/processor/proto/process_state.proto
@@ -39,6 +39,8 @@
 //
 // Author: Jess Gray
 
+syntax = "proto2";
+
 package google_breakpad;
 
 // A proto representation of a process, in a fully-digested state.