diff --git a/configs/mainnet/altair.yaml b/configs/mainnet/altair.yaml
index b7b7603a2..eac4e1c14 100644
--- a/configs/mainnet/altair.yaml
+++ b/configs/mainnet/altair.yaml
@@ -45,8 +45,6 @@ ALTAIR_FORK_EPOCH: 18446744073709551615
 # ---------------------------------------------------------------
 # 1
 MIN_SYNC_COMMITTEE_PARTICIPANTS: 1
-# 2**64 - 1
-MAX_VALID_LIGHT_CLIENT_UPDATES: 18446744073709551615
 
 
 # Validator
diff --git a/configs/minimal/altair.yaml b/configs/minimal/altair.yaml
index 5618af8ff..0300ff1b8 100644
--- a/configs/minimal/altair.yaml
+++ b/configs/minimal/altair.yaml
@@ -45,8 +45,7 @@ ALTAIR_FORK_EPOCH: 18446744073709551615
 # ---------------------------------------------------------------
 # 1
 MIN_SYNC_COMMITTEE_PARTICIPANTS: 1
-# 2**64 - 1
-MAX_VALID_LIGHT_CLIENT_UPDATES: 18446744073709551615
+
 
 # Validator
 # ---------------------------------------------------------------
diff --git a/setup.py b/setup.py
index 37fbd7795..aad834e2c 100644
--- a/setup.py
+++ b/setup.py
@@ -548,7 +548,7 @@ ignored_dependencies = [
     'Bytes1', 'Bytes4', 'Bytes20', 'Bytes32', 'Bytes48', 'Bytes96', 'Bitlist', 'Bitvector',
     'uint8', 'uint16', 'uint32', 'uint64', 'uint128', 'uint256',
     'bytes', 'byte', 'ByteList', 'ByteVector',
-    'Dict', 'dict', 'field', 'ceillog2', 'floorlog2',
+    'Dict', 'dict', 'field', 'ceillog2', 'floorlog2', 'Set'
 ]
 
 
diff --git a/specs/altair/sync-protocol.md b/specs/altair/sync-protocol.md
index ca55c92f7..784ea63b2 100644
--- a/specs/altair/sync-protocol.md
+++ b/specs/altair/sync-protocol.md
@@ -50,7 +50,6 @@ uses sync committees introduced in [this beacon chain extension](./beacon-chain.
 | Name | Value |
 | - | - |
 | `MIN_SYNC_COMMITTEE_PARTICIPANTS` | `1` |
-| `MAX_VALID_LIGHT_CLIENT_UPDATES` | `uint64(2**64 - 1)` |
 
 ## Containers
 
@@ -87,9 +86,10 @@ class LightClientUpdate(Container):
 ### `LightClientStore`
 
 ```python
-class LightClientStore(Container):
+@dataclass
+class LightClientStore(object):
     snapshot: LightClientSnapshot
-    valid_updates: List[LightClientUpdate, MAX_VALID_LIGHT_CLIENT_UPDATES]
+    valid_updates: Set[LightClientUpdate]
 ```
 
 ## Helper functions
@@ -175,7 +175,7 @@ def apply_light_client_update(snapshot: LightClientSnapshot, update: LightClient
 def process_light_client_update(store: LightClientStore, update: LightClientUpdate, current_slot: Slot,
                                 genesis_validators_root: Root) -> None:
     validate_light_client_update(store.snapshot, update, genesis_validators_root)
-    store.valid_updates.append(update)
+    store.valid_updates.add(update)
 
     update_timeout = SLOTS_PER_EPOCH * EPOCHS_PER_SYNC_COMMITTEE_PERIOD
     if (
@@ -186,10 +186,10 @@ def process_light_client_update(store: LightClientStore, update: LightClientUpda
         # Note that (2) means that the current light client design needs finality.
         # It may be changed to re-organizable light client design. See the on-going issue eth2.0-specs#2182.
         apply_light_client_update(store.snapshot, update)
-        store.valid_updates = []
+        store.valid_updates = set()
     elif current_slot > store.snapshot.header.slot + update_timeout:
         # Forced best update when the update timeout has elapsed
         apply_light_client_update(store.snapshot,
                                   max(store.valid_updates, key=lambda update: sum(update.sync_committee_bits)))
-        store.valid_updates = []
+        store.valid_updates = set()
 ```
diff --git a/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py b/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py
index 9b8c35e76..932a46ca5 100644
--- a/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py
+++ b/tests/core/pyspec/eth2spec/test/altair/unittests/test_sync_protocol.py
@@ -32,7 +32,7 @@ def test_process_light_client_update_not_updated(spec, state):
     )
     store = spec.LightClientStore(
         snapshot=pre_snapshot,
-        valid_updates=[]
+        valid_updates=set(),
     )
 
     # Block at slot 1 doesn't increase sync committee period, so it won't update snapshot
@@ -76,7 +76,7 @@ def test_process_light_client_update_not_updated(spec, state):
     spec.process_light_client_update(store, update, state.slot, state.genesis_validators_root)
 
     assert len(store.valid_updates) == 1
-    assert store.valid_updates[0] == update
+    assert store.valid_updates.pop() == update
     assert store.snapshot == pre_snapshot
 
 
@@ -91,7 +91,7 @@ def test_process_light_client_update_timeout(spec, state):
     )
     store = spec.LightClientStore(
         snapshot=pre_snapshot,
-        valid_updates=[]
+        valid_updates=set(),
     )
 
     # Forward to next sync committee period
@@ -156,7 +156,7 @@ def test_process_light_client_update_finality_updated(spec, state):
     )
     store = spec.LightClientStore(
         snapshot=pre_snapshot,
-        valid_updates=[]
+        valid_updates=set(),
     )
 
     # Change finality