diff --git a/litecord/gateway/schemas.py b/litecord/gateway/schemas.py
index 08260b2..4928a37 100644
--- a/litecord/gateway/schemas.py
+++ b/litecord/gateway/schemas.py
@@ -99,6 +99,16 @@ REQ_GUILD_SCHEMA = {
     },
 }
 
+GUILD_SYNC_SCHEMA = {
+    **BASE,
+    **{
+        "d": {
+            "type": "list",
+            "schema": {"type": "snowflake"},
+        }
+    },
+}
+
 
 GW_ACTIVITY = {
     "name": {"type": "string", "required": True},
diff --git a/litecord/gateway/websocket.py b/litecord/gateway/websocket.py
index 091493c..8e58c28 100644
--- a/litecord/gateway/websocket.py
+++ b/litecord/gateway/websocket.py
@@ -64,6 +64,7 @@ from litecord.gateway.schemas import (
     GW_STATUS_UPDATE,
     RESUME_SCHEMA,
     REQ_GUILD_SCHEMA,
+    GUILD_SYNC_SCHEMA,
 )
 
 from litecord.storage import int_
@@ -952,6 +953,7 @@ class GatewayWebsocket:
 
     async def handle_12(self, payload: Dict[str, Any]):
         """Handle OP 12 Guild Sync."""
+        payload = validate(payload, GUILD_SYNC_SCHEMA)
         data = payload["d"]
         gids = await self.user_storage.get_user_guilds(self.state.user_id)