diff --git a/src/fileformat.proto b/src/fileformat.proto
index 21e670a..9486ab9 100644
--- a/src/fileformat.proto
+++ b/src/fileformat.proto
@@ -8,6 +8,8 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
 
 */
 
+syntax = "proto2";
+
 option optimize_for = LITE_RUNTIME;
 option java_package = "crosby.binary";
 package OSMPBF;
diff --git a/src/osmformat.proto b/src/osmformat.proto
index e59bab7..8e4a529 100644
--- a/src/osmformat.proto
+++ b/src/osmformat.proto
@@ -8,6 +8,8 @@ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLI
 
 */
 
+syntax = "proto2";
+
 option optimize_for = LITE_RUNTIME;
 option java_package = "crosby.binary";
 package OSMPBF;