diff --git a/src/r0/room/create_room.rs b/src/r0/room/create_room.rs
index 7af56f2d..7dc1be99 100644
--- a/src/r0/room/create_room.rs
+++ b/src/r0/room/create_room.rs
@@ -27,7 +27,7 @@ ruma_api! {
         ///
         /// Takes precedence over events set by preset, but gets overriden by
         /// name and topic keys.
-        #[serde(skip_serializing_if = "Vec::is_empty")]
+        #[serde(default, skip_serializing_if = "Vec::is_empty")]
         pub initial_state: Vec<InitialStateEvent>,
         /// A list of user IDs to invite to the room.
         ///
diff --git a/src/r0/sync/sync_events.rs b/src/r0/sync/sync_events.rs
index 4220759e..455f26b3 100644
--- a/src/r0/sync/sync_events.rs
+++ b/src/r0/sync/sync_events.rs
@@ -82,7 +82,7 @@ ruma_api! {
         pub device_lists: Option<DeviceLists>,
         /// For each key algorithm, the number of unclaimed one-time keys
         /// currently held on the server for a device.
-        #[serde(skip_serializing_if = "HashMap::is_empty")]
+        #[serde(default, skip_serializing_if = "HashMap::is_empty")]
         pub device_one_time_keys_count: HashMap<KeyAlgorithm, UInt>,
     }