diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index e181fc28c..673c2eeaf 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1373,7 +1373,7 @@ def slash_validator(state: BeaconState, index: ValidatorIndex) -> None:
     Note that this function mutates ``state``.
     """
     validator = state.validator_registry[index]
-    assert state.slot < validator.withdrawable_epoch  # [TO BE REMOVED IN PHASE 2]
+    assert state.slot < get_epoch_start_slot(validator.withdrawable_epoch)  # [TO BE REMOVED IN PHASE 2]
     exit_validator(state, index)
     state.latest_slashed_balances[get_current_epoch(state) % LATEST_SLASHED_EXIT_LENGTH] += get_effective_balance(state, index)