diff --git a/src/protobufs/hostinput.proto b/src/protobufs/hostinput.proto
index 4258d75..02350f8 100644
--- a/src/protobufs/hostinput.proto
+++ b/src/protobufs/hostinput.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 option optimize_for = LITE_RUNTIME;
 
 package HostBuffers;
diff --git a/src/protobufs/transportinstruction.proto b/src/protobufs/transportinstruction.proto
index d4a76f7..b08e7b0 100644
--- a/src/protobufs/transportinstruction.proto
+++ b/src/protobufs/transportinstruction.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 option optimize_for = LITE_RUNTIME;
 
 package TransportBuffers;
diff --git a/src/protobufs/userinput.proto b/src/protobufs/userinput.proto
index 32bceca..5d3a58f 100644
--- a/src/protobufs/userinput.proto
+++ b/src/protobufs/userinput.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 option optimize_for = LITE_RUNTIME;
 
 package ClientBuffers;