diff --git a/specs/core/0_beacon-chain.md b/specs/core/0_beacon-chain.md
index 3863a396d..f12d6646e 100644
--- a/specs/core/0_beacon-chain.md
+++ b/specs/core/0_beacon-chain.md
@@ -1249,7 +1249,7 @@ def activate_validator(state: BeaconState,
     validator.status = ACTIVE
     validator.latest_status_change_slot = state.slot
     state.validator_registry_delta_chain_tip = get_new_validator_registry_delta_chain_tip(
-        validator_registry_delta_chain_tip=validator_registry_delta_chain_tip,
+        validator_registry_delta_chain_tip=state.validator_registry_delta_chain_tip,
         index=index,
         pubkey=validator.pubkey,
         flag=ACTIVATION,