diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index f6427f1d4..df9ace80b 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -2416,6 +2416,8 @@ def process_transfer(state: BeaconState, transfer: Transfer) -> None:
         get_balance(state, transfer.sender) == transfer.amount + transfer.fee or
         get_balance(state, transfer.sender) >= transfer.amount + transfer.fee + MIN_DEPOSIT_AMOUNT
     )
+    # No self-transfers (to enforce >= MIN_DEPOSIT_AMOUNT or zero balance invariant)
+    assert transfer.sender != transfer.recipient
     # A transfer is valid in only one slot
     assert state.slot == transfer.slot
     # Only withdrawn or not-yet-deposited accounts can transfer