diff --git a/update_metadata.proto b/update_metadata.proto
index 9175c42..ad377c7 100644
--- a/update_metadata.proto
+++ b/update_metadata.proto
@@ -164,11 +164,11 @@
 
     // On minor version 3 or newer and on major version 2 or newer, these
     // operations are supported:
-    ZERO = 6;  // Write zeros in the destination.
-    DISCARD = 7;  // Discard the destination blocks, reading as undefined.
     REPLACE_XZ = 8; // Replace destination extents w/ attached xz data.
 
     // On minor version 4 or newer, these operations are supported:
+    ZERO = 6;  // Write zeros in the destination.
+    DISCARD = 7;  // Discard the destination blocks, reading as undefined.
     PUFFDIFF = 9;  // The data is in puffdiff format.
     BROTLI_BSDIFF = 10;  // Like SOURCE_BSDIFF, but compressed with brotli.
   }