diff --git a/beacon_chain/spec/datatypes/altair.nim b/beacon_chain/spec/datatypes/altair.nim
index f7cd21efc..0098e6549 100644
--- a/beacon_chain/spec/datatypes/altair.nim
+++ b/beacon_chain/spec/datatypes/altair.nim
@@ -51,7 +51,7 @@ const
   TARGET_AGGREGATORS_PER_SYNC_SUBCOMMITTEE* = 16
   SYNC_COMMITTEE_SUBNET_COUNT* = 4
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#constants
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#constants
   # All of these indices are rooted in `BeaconState`.
   # The first member (`genesis_time`) is 32, subsequent members +1 each.
   # If there are ever more than 32 members in `BeaconState`, indices change!
@@ -69,7 +69,7 @@ const
   INACTIVITY_SCORE_BIAS* = 4
   INACTIVITY_SCORE_RECOVERY_RATE* = 16
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#misc
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#misc
   # MIN_SYNC_COMMITTEE_PARTICIPANTS defined in presets
   UPDATE_TIMEOUT* = SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD
 
@@ -157,7 +157,7 @@ type
 
   ### Modified/overloaded
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#lightclientupdate
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#lightclientupdate
   LightClientUpdate* = object
     attested_header*: BeaconBlockHeader ##\
     ## The beacon block header that is attested to by the sync committee
@@ -177,7 +177,7 @@ type
     fork_version*: Version ##\
     ## Fork version for the aggregate signature
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#lightclientstore
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#lightclientstore
   LightClientStore* = object
     finalized_header*: BeaconBlockHeader ##\
     ## Beacon block header that is finalized
diff --git a/beacon_chain/spec/helpers.nim b/beacon_chain/spec/helpers.nim
index 1d1728f2d..232f7eb10 100644
--- a/beacon_chain/spec/helpers.nim
+++ b/beacon_chain/spec/helpers.nim
@@ -475,7 +475,7 @@ func has_flag*(flags: ParticipationFlags, flag_index: int): bool =
   let flag = ParticipationFlags(1'u8 shl flag_index)
   (flags and flag) == flag
 
-# https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#get_subtree_index
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#get_subtree_index
 func get_subtree_index*(idx: GeneralizedIndex): uint64 =
   doAssert idx > 0
   uint64(idx mod (type(idx)(1) shl log2trunc(idx)))
diff --git a/beacon_chain/spec/light_client_sync.nim b/beacon_chain/spec/light_client_sync.nim
index 8f0bd2e82..5a672758c 100644
--- a/beacon_chain/spec/light_client_sync.nim
+++ b/beacon_chain/spec/light_client_sync.nim
@@ -12,24 +12,28 @@ import
   datatypes/altair,
   helpers
 
-# https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#get_active_header
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#get_active_header
+func is_finality_update(update: altair.LightClientUpdate): bool =
+  not update.finalized_header.isZeroMemory
+
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#get_active_header
 func get_active_header(update: altair.LightClientUpdate): BeaconBlockHeader =
   # The "active header" is the header that the update is trying to convince
   # us to accept. If a finalized header is present, it's the finalized
   # header, otherwise it's the attested header
-  if not update.finalized_header.isZeroMemory:
+  if update.is_finality_update:
     update.finalized_header
   else:
     update.attested_header
 
-# https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#get_safety_threshold
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#get_safety_threshold
 func get_safety_threshold(store: LightClientStore): uint64 =
   max(
     store.previous_max_active_participants,
     store.current_max_active_participants
   ) div 2
 
-# https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#validate_light_client_update
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#validate_light_client_update
 proc validate_light_client_update*(
     store: LightClientStore,
     update: altair.LightClientUpdate,
@@ -51,7 +55,7 @@ proc validate_light_client_update*(
 
   # Verify that the `finalized_header`, if present, actually is the finalized
   # header saved in the state of the `attested header`
-  if update.finalized_header.isZeroMemory:
+  if not update.is_finality_update:
     if not update.finality_branch.isZeroMemory:
       return false
   else:
@@ -100,7 +104,7 @@ proc validate_light_client_update*(
   blsFastAggregateVerify(
     participant_pubkeys, signing_root.data, sync_aggregate.sync_committee_signature)
 
-# https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#apply_light_client_update
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#apply_light_client_update
 func apply_light_client_update(
     store: var LightClientStore,
     update: altair.LightClientUpdate) =
@@ -112,8 +116,10 @@ func apply_light_client_update(
     store.current_sync_committee = store.next_sync_committee
     store.next_sync_committee = update.next_sync_committee
   store.finalized_header = active_header
+  if store.finalized_header.slot > store.optimistic_header.slot:
+    store.optimistic_header = store.finalized_header
 
-# https://github.com/ethereum/consensus-specs/blob/v1.1.9/specs/altair/sync-protocol.md#process_light_client_update
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/specs/altair/sync-protocol.md#process_light_client_update
 proc process_light_client_update*(
     store: var LightClientStore,
     update: altair.LightClientUpdate,
@@ -147,7 +153,7 @@ proc process_light_client_update*(
 
   # Update finalized header
   if  sum_sync_committee_bits * 3 >= len(sync_committee_bits) * 2 and
-      not update.finalized_header.isZeroMemory:
+      update.is_finality_update:
     # Normal update through 2/3 threshold
     apply_light_client_update(store, update)
     store.best_valid_update = none(altair.LightClientUpdate)
diff --git a/tests/consensus_spec/altair/test_fixture_sync_protocol.nim b/tests/consensus_spec/altair/test_fixture_sync_protocol.nim
index 548f0564e..244449abb 100644
--- a/tests/consensus_spec/altair/test_fixture_sync_protocol.nim
+++ b/tests/consensus_spec/altair/test_fixture_sync_protocol.nim
@@ -74,7 +74,7 @@ let full_sync_committee_bits = block:
   res.bytes.fill(byte.high)
   res
 
-# https://github.com/ethereum/consensus-specs/blob/v1.1.9/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py#L24-L33
+# https://github.com/ethereum/consensus-specs/blob/v1.1.10/tests/core/pyspec/eth2spec/test/helpers/light_client.py#L6-L15
 func initialize_light_client_store(state: auto): LightClientStore =
   LightClientStore(
     finalized_header: BeaconBlockHeader(),
@@ -94,7 +94,7 @@ suite "EF - Altair - Unittests - Sync protocol" & preset():
       res
     genesisState = newClone(initGenesisState(cfg = cfg))
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py#L36-L90
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.10/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py#L27-L69
   test "test_process_light_client_update_not_timeout":
     let forked = assignClone(genesisState[])
     template state: untyped {.inject.} = forked[].altairData.data
@@ -151,7 +151,7 @@ suite "EF - Altair - Unittests - Sync protocol" & preset():
       store.finalized_header == pre_store_finalized_header
       store.best_valid_update.get == update
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py#L93-L154
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.10/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py#L72-L121
   test "process_light_client_update_timeout":
     let forked = assignClone(genesisState[])
     template state: untyped {.inject.} = forked[].altairData.data
@@ -215,7 +215,7 @@ suite "EF - Altair - Unittests - Sync protocol" & preset():
       store.finalized_header == pre_store_finalized_header
       store.best_valid_update.get == update
 
-  # https://github.com/ethereum/consensus-specs/blob/v1.1.9/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py#L157-L224
+  # https://github.com/ethereum/consensus-specs/blob/v1.1.10/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py#L124-L179
   test "process_light_client_update_finality_updated":
     let forked = assignClone(genesisState[])
     template state: untyped {.inject.} = forked[].altairData.data