diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 91c1aecf8..ee5f16dd9 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -418,11 +418,16 @@ Unless otherwise indicated, code appearing in `this style` is to be interpreted
 
 #### `BeaconBlockBody`
 
+`ProofOfCustodySeedChange`, `ProofOfCustodyChallenge`, `ProofOfCustodyResponse` defined in phase 1; for now put dummy classes as these lists will remain empty throughout phase 0.
+
 ```python
 {
     'proposer_slashings': [ProposerSlashing],
     'casper_slashings': [CasperSlashing],
     'attestations': [Attestation],
+    'poc_seed_changes': [ProofOfCustodySeedChange],
+    'poc_challenges': [ProofOfCustodyChallenge],
+    'poc_responses': [ProofOfCustodyResponse],
     'deposits': [Deposit],
     'exits': [Exit],
 }
@@ -465,6 +470,16 @@ Unless otherwise indicated, code appearing in `this style` is to be interpreted
     'persistent_committees': [['uint24']],
     'persistent_committee_reassignments': [ShardReassignmentRecord],
 
+    # Proof of custody
+    # Placeholders for now; ProofOfCustodyChallenge is defined in phase 1, implementers can
+    # put a dummy class in for now, as the list will remain empty throughout phase 0
+    'poc_challenges': [ProofOfCustodyChallenge],
+    # Proof of custody commitment
+    'poc_commitment': 'hash32',
+    # Slot the proof of custody seed was last changed
+    'last_poc_change_slot': 'uint64',
+    'second_last_poc_change_slot': 'uint64',
+
     # Finality
     'previous_justified_slot': 'uint64',
     'justified_slot': 'uint64',
@@ -1533,6 +1548,10 @@ For each `exit` in `block.body.exits`:
 * Verify that `bls_verify(pubkey=validator.pubkey, message=ZERO_HASH, signature=exit.signature, domain=get_domain(state.fork_data, exit.slot, DOMAIN_EXIT))`.
 * Run `update_validator_status(state, validator_index, new_status=ACTIVE_PENDING_EXIT)`.
 
+#### Miscellaneous
+
+[TO BE REMOVED IN PHASE 1] Verify that `len(block.body.poc_seed_changes) == len(block.body.poc_challenges) == len(block.body.poc_responses) == 0`.
+
 ## Per-epoch processing
 
 The steps below happen when `state.slot % EPOCH_LENGTH == 0`.