diff --git a/src/engine/experimental/blob-extension.md b/src/engine/experimental/blob-extension.md
index b4cbbc6c3..e9d8779a5 100644
--- a/src/engine/experimental/blob-extension.md
+++ b/src/engine/experimental/blob-extension.md
@@ -55,6 +55,8 @@ The fields are encoded as follows:
 - `proofs`: `Array of DATA` - Array of `KZGProof` as defined in [EIP-4844](https://eips.ethereum.org/EIPS/eip-4844), 48 bytes each (`DATA`).
 - `blobs`: `Array of DATA` - Array of blobs, each blob is `FIELD_ELEMENTS_PER_BLOB * BYTES_PER_FIELD_ELEMENT = 4096 * 32 = 131072` bytes (`DATA`) representing a SSZ-encoded `Blob` as defined in [EIP-4844](https://eips.ethereum.org/EIPS/eip-4844)
 
+All of the above three arrays **MUST** be of same length.
+
 ## Methods
 
 ### engine_newPayloadV3