diff --git a/protob/config.proto b/protob/config.proto
index b7ffedd85..fe44a0dc3 100644
--- a/protob/config.proto
+++ b/protob/config.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 /**
  * Configuration format for TREZOR plugin
  */
diff --git a/protob/messages.proto b/protob/messages.proto
index e31d5b0fe..516391fa7 100644
--- a/protob/messages.proto
+++ b/protob/messages.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 /**
  * Messages for TREZOR communication
  */
diff --git a/protob/storage.proto b/protob/storage.proto
index 4b707d15d..764fcdfb9 100644
--- a/protob/storage.proto
+++ b/protob/storage.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 /**
  * Storage area of TREZOR
  */
diff --git a/protob/types.proto b/protob/types.proto
index fa382e3e5..95695e368 100644
--- a/protob/types.proto
+++ b/protob/types.proto
@@ -1,3 +1,5 @@
+syntax = "proto2";
+
 /**
  * Types for TREZOR communication
  *