diff --git a/substrate/tendermint/primitives/src/lib.rs b/substrate/tendermint/primitives/src/lib.rs
index 50cc78d1..b5a1d6b2 100644
--- a/substrate/tendermint/primitives/src/lib.rs
+++ b/substrate/tendermint/primitives/src/lib.rs
@@ -4,6 +4,7 @@ use sp_core::sr25519::Public;
 use sp_std::vec::Vec;
 
 sp_api::decl_runtime_apis! {
+  /// TendermintApi trait for runtimes to implement.
   pub trait TendermintApi {
     /// Current session number. A session is NOT a fixed length of blocks, yet rather a continuous
     /// set of validators.