diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index ceca509620..9571c23db3 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -2305,8 +2305,8 @@ def process_proposer_slashing(state: BeaconState,
     Note that this function mutates ``state``.
     """
     proposer = state.validator_registry[proposer_slashing.proposer_index]
-    # Verify that the slot is the same
-    assert proposer_slashing.header_1.slot == proposer_slashing.header_2.slot
+    # Verify that the epoch is the same
+    assert slot_to_epoch(proposer_slashing.header_1.slot) == slot_to_epoch(proposer_slashing.header_2.slot)
     # But the headers are different
     assert proposer_slashing.header_1 != proposer_slashing.header_2
     # Proposer is not yet slashed