diff --git a/zcash_client_backend/proto/compact_formats.proto b/zcash_client_backend/proto/compact_formats.proto
index 077537c60..eac2b2f2f 100644
--- a/zcash_client_backend/proto/compact_formats.proto
+++ b/zcash_client_backend/proto/compact_formats.proto
@@ -22,6 +22,8 @@ message CompactBlock {
     uint32 time = 5;            // Unix epoch time when the block was mined
     bytes header = 6;           // (hash, prevHash, and time) OR (full header)
     repeated CompactTx vtx = 7; // zero or more compact transactions from this block
+    uint32 saplingCommitmentTreeSize = 8; // the size of the Sapling note commitment tree as of the end of this block
+    uint32 orchardCommitmentTreeSize = 9; // the size of the Orchard note commitment tree as of the end of this block
 }
 
 // CompactTx contains the minimum information for a wallet to know if this transaction
diff --git a/zcash_client_backend/src/proto/compact_formats.rs b/zcash_client_backend/src/proto/compact_formats.rs
index 056764b78..c8d45173c 100644
--- a/zcash_client_backend/src/proto/compact_formats.rs
+++ b/zcash_client_backend/src/proto/compact_formats.rs
@@ -26,6 +26,12 @@ pub struct CompactBlock {
     /// zero or more compact transactions from this block
     #[prost(message, repeated, tag = "7")]
     pub vtx: ::prost::alloc::vec::Vec<CompactTx>,
+    /// the size of the Sapling note commitment tree as of the end of this block
+    #[prost(uint32, tag = "8")]
+    pub sapling_commitment_tree_size: u32,
+    /// the size of the Orchard note commitment tree as of the end of this block
+    #[prost(uint32, tag = "9")]
+    pub orchard_commitment_tree_size: u32,
 }
 /// CompactTx contains the minimum information for a wallet to know if this transaction
 /// is relevant to it (either pays to it or spends from it) via shielded elements