diff --git a/crates/ruma-client-api/CHANGELOG.md b/crates/ruma-client-api/CHANGELOG.md
index 244dfb06..a05f50de 100644
--- a/crates/ruma-client-api/CHANGELOG.md
+++ b/crates/ruma-client-api/CHANGELOG.md
@@ -1,5 +1,17 @@
 # [unreleased]
 
+Improvements:
+
+* Add unstable support for reasons in the membership endpoints:
+  ```rust
+  r0::membership::{
+    join_room_by_id,
+    join_room_by_id_or_alias,
+    invite_user,
+    unban_user
+  }
+  ```
+
 # 0.12.3
 
 * Add a `feature = "compat"` workaround for Element failing on `GET /_matrix/client/r0/account/3pid`
diff --git a/crates/ruma-client-api/src/r0/membership/invite_user.rs b/crates/ruma-client-api/src/r0/membership/invite_user.rs
index b4558adf..997091bf 100644
--- a/crates/ruma-client-api/src/r0/membership/invite_user.rs
+++ b/crates/ruma-client-api/src/r0/membership/invite_user.rs
@@ -30,8 +30,14 @@ ruma_api! {
         pub room_id: &'a RoomId,
 
         /// The user to invite.
-        #[ruma_api(body)]
+        #[serde(flatten)]
         pub recipient: InvitationRecipient<'a>,
+
+        /// Optional reason for inviting the user.
+        #[cfg(feature = "unstable-pre-spec")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "unstable-pre-spec")))]
+        #[serde(skip_serializing_if = "Option::is_none")]
+        pub reason: Option<&'a str>,
     }
 
     #[derive(Default)]
@@ -43,7 +49,12 @@ ruma_api! {
 impl<'a> Request<'a> {
     /// Creates a new `Request` with the given room ID and invitation recipient.
     pub fn new(room_id: &'a RoomId, recipient: InvitationRecipient<'a>) -> Self {
-        Self { room_id, recipient }
+        Self {
+            room_id,
+            recipient,
+            #[cfg(feature = "unstable-pre-spec")]
+            reason: None,
+        }
     }
 }
 
diff --git a/crates/ruma-client-api/src/r0/membership/join_room_by_id.rs b/crates/ruma-client-api/src/r0/membership/join_room_by_id.rs
index bc8d53d5..5d6ac07d 100644
--- a/crates/ruma-client-api/src/r0/membership/join_room_by_id.rs
+++ b/crates/ruma-client-api/src/r0/membership/join_room_by_id.rs
@@ -24,6 +24,12 @@ ruma_api! {
         /// party identity which has been invited to the room.
         #[serde(skip_serializing_if = "Option::is_none")]
         pub third_party_signed: Option<ThirdPartySigned<'a>>,
+
+        /// Optional reason for joining the room.
+        #[cfg(feature = "unstable-pre-spec")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "unstable-pre-spec")))]
+        #[serde(skip_serializing_if = "Option::is_none")]
+        pub reason: Option<&'a str>,
     }
 
     response: {
@@ -37,7 +43,12 @@ ruma_api! {
 impl<'a> Request<'a> {
     /// Creates a new `Request` with the given room id.
     pub fn new(room_id: &'a RoomId) -> Self {
-        Self { room_id, third_party_signed: None }
+        Self {
+            room_id,
+            third_party_signed: None,
+            #[cfg(feature = "unstable-pre-spec")]
+            reason: None,
+        }
     }
 }
 
diff --git a/crates/ruma-client-api/src/r0/membership/join_room_by_id_or_alias.rs b/crates/ruma-client-api/src/r0/membership/join_room_by_id_or_alias.rs
index f2af3b5f..11e4535a 100644
--- a/crates/ruma-client-api/src/r0/membership/join_room_by_id_or_alias.rs
+++ b/crates/ruma-client-api/src/r0/membership/join_room_by_id_or_alias.rs
@@ -30,6 +30,12 @@ ruma_api! {
         /// party identity which has been invited to the room.
         #[serde(skip_serializing_if = "Option::is_none")]
         pub third_party_signed: Option<ThirdPartySigned<'a>>,
+
+        /// Optional reason for joining the room.
+        #[cfg(feature = "unstable-pre-spec")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "unstable-pre-spec")))]
+        #[serde(skip_serializing_if = "Option::is_none")]
+        pub reason: Option<&'a str>,
     }
 
     response: {
@@ -43,7 +49,13 @@ ruma_api! {
 impl<'a> Request<'a> {
     /// Creates a new `Request` with the given room ID or alias ID.
     pub fn new(room_id_or_alias: &'a RoomIdOrAliasId) -> Self {
-        Self { room_id_or_alias, server_name: &[], third_party_signed: None }
+        Self {
+            room_id_or_alias,
+            server_name: &[],
+            third_party_signed: None,
+            #[cfg(feature = "unstable-pre-spec")]
+            reason: None,
+        }
     }
 }
 
diff --git a/crates/ruma-client-api/src/r0/membership/unban_user.rs b/crates/ruma-client-api/src/r0/membership/unban_user.rs
index 2952ae6d..97cc8866 100644
--- a/crates/ruma-client-api/src/r0/membership/unban_user.rs
+++ b/crates/ruma-client-api/src/r0/membership/unban_user.rs
@@ -20,6 +20,12 @@ ruma_api! {
 
         /// The user to unban.
         pub user_id: &'a UserId,
+
+        /// Optional reason for unbanning the user.
+        #[cfg(feature = "unstable-pre-spec")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "unstable-pre-spec")))]
+        #[serde(skip_serializing_if = "Option::is_none")]
+        pub reason: Option<&'a str>,
     }
 
     #[derive(Default)]
@@ -31,7 +37,12 @@ ruma_api! {
 impl<'a> Request<'a> {
     /// Creates a new `Request` with the given room id and room id.
     pub fn new(room_id: &'a RoomId, user_id: &'a UserId) -> Self {
-        Self { room_id, user_id }
+        Self {
+            room_id,
+            user_id,
+            #[cfg(feature = "unstable-pre-spec")]
+            reason: None,
+        }
     }
 }