diff --git a/src/action-item.proto b/src/action-item.proto
index 1bba70f..7bb6f21 100644
--- a/src/action-item.proto
+++ b/src/action-item.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 message ActionItem
 {
   enum ActionType
diff --git a/src/file-item.proto b/src/file-item.proto
index 4840cec..4e2a430 100644
--- a/src/file-item.proto
+++ b/src/file-item.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 message FileItem
 {
   required string filename = 2;
diff --git a/src/sync-state.proto b/src/sync-state.proto
index 410726b..759b7d3 100644
--- a/src/sync-state.proto
+++ b/src/sync-state.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 message SyncState
 {
   required bytes name = 1;