diff --git a/crates/ruma-common/src/directory.rs b/crates/ruma-common/src/directory.rs
index b31ba7a2..d6d34fda 100644
--- a/crates/ruma-common/src/directory.rs
+++ b/crates/ruma-common/src/directory.rs
@@ -109,7 +109,7 @@ impl From<PublicRoomsChunkInit> for PublicRoomsChunk {
     }
 }
 
-/// A filter for public rooms lists
+/// A filter for public rooms lists.
 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
 pub struct Filter {
@@ -121,6 +121,7 @@ pub struct Filter {
     ///
     /// Includes all room types if it is empty.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
+    #[cfg_attr(feature = "compat", serde(deserialize_with = "crate::serde::none_as_default"))]
     pub room_types: Vec<RoomTypeFilter>,
 }
 
diff --git a/crates/ruma-common/src/serde.rs b/crates/ruma-common/src/serde.rs
index 28e4b81d..06475ede 100644
--- a/crates/ruma-common/src/serde.rs
+++ b/crates/ruma-common/src/serde.rs
@@ -5,7 +5,7 @@
 //!
 //! [serde_urlencoded]: https://github.com/nox/serde_urlencoded
 
-use serde::{de, Deserialize};
+use serde::{de, Deserialize, Deserializer};
 use serde_json::{value::RawValue as RawJsonValue, Value as JsonValue};
 
 pub mod base64;
@@ -40,6 +40,15 @@ pub fn is_default<T: Default + PartialEq>(val: &T) -> bool {
     *val == T::default()
 }
 
+/// Deserialize a `T` via `Option<T>`, falling back to `T::default()`.
+pub fn none_as_default<'de, D, T>(deserializer: D) -> Result<T, D::Error>
+where
+    D: Deserializer<'de>,
+    T: Default + Deserialize<'de>,
+{
+    Ok(Option::deserialize(deserializer)?.unwrap_or_default())
+}
+
 /// Simply returns `true`.
 ///
 /// Useful for `#[serde(default = ...)]`.