diff --git a/substrate/substrate/primitives/src/block.rs b/substrate/substrate/primitives/src/block.rs
index 619920b40f..10315d2309 100644
--- a/substrate/substrate/primitives/src/block.rs
+++ b/substrate/substrate/primitives/src/block.rs
@@ -90,6 +90,7 @@ impl Slicable for Digest {
 
 impl NonTrivialSlicable for Digest { }
 
+/// Generic types to be specialised later.
 pub mod generic {
 	use super::{Header, Slicable, Input, NonTrivialSlicable};