diff --git a/src/service/account_data.rs b/src/service/account_data.rs
index c755ece1..7b51b421 100644
--- a/src/service/account_data.rs
+++ b/src/service/account_data.rs
@@ -48,6 +48,9 @@ impl Service {
     }
 
     /// Returns all changes to the account data that happened after `since`.
+    ///
+    /// When there have been multiple changes to the same event type, returned
+    /// map contains the most recent value.
     #[tracing::instrument(skip(self, room_id, user_id, since))]
     pub(crate) fn changes_since(
         &self,
diff --git a/src/service/account_data/data.rs b/src/service/account_data/data.rs
index 04d4bf76..868881c8 100644
--- a/src/service/account_data/data.rs
+++ b/src/service/account_data/data.rs
@@ -28,6 +28,9 @@ pub(crate) trait Data: Send + Sync {
     ) -> Result<Option<Box<serde_json::value::RawValue>>>;
 
     /// Returns all changes to the account data that happened after `since`.
+    ///
+    /// When there have been multiple changes to the same event type, returned
+    /// map contains the most recent value.
     fn changes_since(
         &self,
         room_id: Option<&RoomId>,