diff --git a/Cargo.toml b/Cargo.toml
index 4eaf5c4586..a90b587382 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -150,6 +150,7 @@ etcd-client = { git = "https://github.com/GreptimeTeam/etcd-client", rev = "f62d
 fst = "0.4.7"
 futures = "0.3"
 futures-util = "0.3"
+# protobuf definitions
 greptime-proto = { git = "https://github.com/GreptimeTeam/greptime-proto.git", rev = "0423fa30203187c75e2937a668df1da699c8b96c" }
 hex = "0.4"
 http = "1"