diff --git a/Cargo.toml b/Cargo.toml
index cfbef630..154cbbb4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -31,6 +31,7 @@ enum_glob_use = "warn"
 error_impl_error = "warn"
 explicit_into_iter_loop = "warn"
 filetype_is_file = "warn"
+flat_map_option = "warn"
 float_cmp_const = "warn"
 format_push_string = "warn"
 get_unwrap = "warn"
diff --git a/src/api/client_server/sync.rs b/src/api/client_server/sync.rs
index 4004bc42..d1536a81 100644
--- a/src/api/client_server/sync.rs
+++ b/src/api/client_server/sync.rs
@@ -1559,7 +1559,7 @@ pub(crate) async fn sync_events_v4_route(
 
         let required_state = required_state_request
             .iter()
-            .flat_map(|state| {
+            .filter_map(|state| {
                 services()
                     .rooms
                     .state_accessor
@@ -1577,7 +1577,7 @@ pub(crate) async fn sync_events_v4_route(
             .room_members(room_id)
             .filter_map(|r| r.ok())
             .filter(|member| member != &sender_user)
-            .flat_map(|member| {
+            .filter_map(|member| {
                 services()
                     .rooms
                     .state_accessor