diff --git a/specs/phase0/fork-choice.md b/specs/phase0/fork-choice.md
index 43dac92d1..66a87021c 100644
--- a/specs/phase0/fork-choice.md
+++ b/specs/phase0/fork-choice.md
@@ -467,6 +467,8 @@ def on_attestation(store: Store, attestation: Attestation, is_from_block: bool=F
 
 #### `on_attester_slashing`
 
+*Note*: `on_attester_slashing` should be called while syncing and a node MUST maintain the equivocation set of `AttesterSlashing`s from at least the last finalized checkpoint
+
 ```python
 def on_attester_slashing(store: Store, attester_slashing: AttesterSlashing) -> None:
     """