diff --git a/specs/deneb/p2p-interface.md b/specs/deneb/p2p-interface.md
index f857ffdf13..a81e5d0bb6 100644
--- a/specs/deneb/p2p-interface.md
+++ b/specs/deneb/p2p-interface.md
@@ -148,6 +148,7 @@ This topic is used to propagate signed blob sidecars, where each blob index maps
 
 The following validations MUST pass before forwarding the `signed_blob_sidecar` on the network, assuming the alias `sidecar = signed_blob_sidecar.message`:
 
+- _[REJECT]_ The sidecar's index is consistent with `MAX_BLOBS_PER_BLOCK` -- i.e. `sidecar.index < MAX_BLOBS_PER_BLOCK`.
 - _[REJECT]_ The sidecar is for the correct subnet -- i.e. `compute_subnet_for_blob_sidecar(sidecar.index) == subnet_id`.
 - _[IGNORE]_ The sidecar is not from a future slot (with a `MAXIMUM_GOSSIP_CLOCK_DISPARITY` allowance) -- i.e. validate that `sidecar.slot <= current_slot` (a client MAY queue future sidecars for processing at the appropriate slot).
 - _[IGNORE]_ The sidecar is from a slot greater than the latest finalized slot -- i.e. validate that `sidecar.slot > compute_start_slot_at_epoch(state.finalized_checkpoint.epoch)`