diff --git a/ruma-common/src/directory.rs b/ruma-common/src/directory.rs
index eb723a8b..85d61028 100644
--- a/ruma-common/src/directory.rs
+++ b/ruma-common/src/directory.rs
@@ -12,8 +12,12 @@ use serde::{
 
 use serde_json::Value as JsonValue;
 
-/// A chunk of a room list response, describing one room
+/// A chunk of a room list response, describing one room.
+///
+/// To create an instance of this type, first create a `PublicRoomsChunkInit` and convert it via
+/// `PublicRoomsChunk::from` / `.into()`.
 #[derive(Clone, Debug, Deserialize, Serialize)]
+#[non_exhaustive]
 pub struct PublicRoomsChunk {
     /// Aliases of the room.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
@@ -50,17 +54,66 @@ pub struct PublicRoomsChunk {
     pub avatar_url: Option<String>,
 }
 
+/// Initial set of mandatory fields of `PublicRoomsChunk`.
+///
+/// This struct will not be updated even if additional fields are added to `PublicRoomsChunk` in a
+/// new (non-breaking) release of the Matrix specification.
+#[derive(Debug)]
+pub struct PublicRoomsChunkInit {
+    /// The number of members joined to the room.
+    pub num_joined_members: UInt,
+
+    /// The ID of the room.
+    pub room_id: RoomId,
+
+    /// Whether the room may be viewed by guest users without joining.
+    pub world_readable: bool,
+
+    /// Whether guest users may join the room and participate in it.
+    ///
+    /// If they can, they will be subject to ordinary power level rules like any other user.
+    pub guest_can_join: bool,
+}
+
+impl From<PublicRoomsChunkInit> for PublicRoomsChunk {
+    fn from(init: PublicRoomsChunkInit) -> Self {
+        let PublicRoomsChunkInit { num_joined_members, room_id, world_readable, guest_can_join } =
+            init;
+
+        Self {
+            aliases: Vec::new(),
+            canonical_alias: None,
+            name: None,
+            num_joined_members,
+            room_id,
+            topic: None,
+            world_readable,
+            guest_can_join,
+            avatar_url: None,
+        }
+    }
+}
+
 /// A filter for public rooms lists
-#[derive(Clone, Debug, Deserialize, Serialize)]
+#[derive(Clone, Debug, Default, Deserialize, Serialize)]
+#[non_exhaustive]
 pub struct Filter {
     /// A string to search for in the room metadata, e.g. name, topic, canonical alias etc.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub generic_search_term: Option<String>,
 }
 
+impl Filter {
+    /// Creates an empty `Filter`.
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
 /// Information about which networks/protocols from application services on the
 /// homeserver from which to request rooms.
 #[derive(Clone, Debug, PartialEq, Eq)]
+#[non_exhaustive]
 pub enum RoomNetwork {
     /// Return rooms from the Matrix network.
     Matrix,
diff --git a/ruma-common/src/encryption.rs b/ruma-common/src/encryption.rs
index ec3d3118..e5550fb2 100644
--- a/ruma-common/src/encryption.rs
+++ b/ruma-common/src/encryption.rs
@@ -8,7 +8,8 @@ use ruma_identifiers::{DeviceIdBox, DeviceKeyId, EventEncryptionAlgorithm, UserI
 use serde::{Deserialize, Serialize};
 
 /// Identity keys for a device.
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Clone, Debug, Deserialize, Serialize)]
+#[non_exhaustive]
 pub struct DeviceKeys {
     /// The ID of the user the device belongs to. Must match the user ID used when logging in.
     pub user_id: UserId,
@@ -27,13 +28,40 @@ pub struct DeviceKeys {
 
     /// Additional data added to the device key information by intermediate servers, and
     /// not covered by the signatures.
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub unsigned: Option<UnsignedDeviceInfo>,
+    #[serde(skip_serializing_if = "UnsignedDeviceInfo::is_empty")]
+    pub unsigned: UnsignedDeviceInfo,
+}
+
+impl DeviceKeys {
+    /// Creates a new `DeviceKeys` from the given user id, device id, algorithms, keys and
+    /// signatures.
+    pub fn new(
+        user_id: UserId,
+        device_id: DeviceIdBox,
+        algorithms: Vec<EventEncryptionAlgorithm>,
+        keys: BTreeMap<DeviceKeyId, String>,
+        signatures: BTreeMap<UserId, BTreeMap<DeviceKeyId, String>>,
+    ) -> Self {
+        Self { user_id, device_id, algorithms, keys, signatures, unsigned: Default::default() }
+    }
 }
 
 /// Additional data added to device key information by intermediate servers.
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Clone, Debug, Default, Deserialize, Serialize)]
 pub struct UnsignedDeviceInfo {
     /// The display name which the user set on the device.
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub device_display_name: Option<String>,
 }
+
+impl UnsignedDeviceInfo {
+    /// Creates an empty `UnsignedDeviceInfo`.
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    /// Checks whether all fields are empty / `None`.
+    pub fn is_empty(&self) -> bool {
+        self.device_display_name.is_none()
+    }
+}
diff --git a/ruma-common/src/push.rs b/ruma-common/src/push.rs
index 8bd3aafe..033650e3 100644
--- a/ruma-common/src/push.rs
+++ b/ruma-common/src/push.rs
@@ -18,9 +18,6 @@ pub use self::{
 ///
 /// For example, some rules may only be applied for messages from a particular sender, a particular
 /// room, or by default. The push ruleset contains the entire set of scopes and rules.
-///
-/// To create an instance of this type, use its `Default` implementation and set the fields you
-/// need.
 #[derive(Clone, Debug, Default, Deserialize, Serialize)]
 #[non_exhaustive]
 pub struct Ruleset {
@@ -45,6 +42,13 @@ pub struct Ruleset {
     pub underride: Vec<ConditionalPushRule>,
 }
 
+impl Ruleset {
+    /// Creates an empty `Ruleset`.
+    pub fn new() -> Self {
+        Default::default()
+    }
+}
+
 /// A push rule is a single rule that states under what conditions an event should be passed onto a
 /// push gateway and how the notification should be presented.
 ///