diff --git a/src/fileformat.proto b/src/fileformat.proto
index 54be8fe..7cc76ab 100644
--- a/src/fileformat.proto
+++ b/src/fileformat.proto
@@ -15,8 +15,8 @@ message Blob {
   // Possible compressed versions of the data.
   optional bytes zlib_data = 3;
 
-  // PROPOSED feature for LZMA compressed data.
-  // optional bytes lzma_data = 4; // Do not change this tag number.
+  // PROPOSED feature for LZMA compressed data. SUPPORT IS NOT REQUIRED.
+  optional bytes lzma_data = 4;
 
   // Formerly used for bzip2 compressed data. Depreciated in 2010.
   optional bytes OBSOLETE_bzip2_data = 5 [deprecated=true]; // Don't reuse this tag number.