diff --git a/ruma-client-api/src/error.rs b/ruma-client-api/src/error.rs
index 0b3605f5..5fea2791 100644
--- a/ruma-client-api/src/error.rs
+++ b/ruma-client-api/src/error.rs
@@ -20,7 +20,14 @@ pub enum ErrorKind {
     /// M_UNKNOWN_TOKEN
     #[serde(rename = "M_UNKNOWN_TOKEN")]
     #[strum(to_string = "M_UNKNOWN_TOKEN")]
-    UnknownToken,
+    UnknownToken {
+        /// If this is `true`, the client can acquire a new access token by specifying the device ID
+        /// it is already using to the login API. For more information, see [the spec].
+        ///
+        /// [the spec]: https://matrix.org/docs/spec/client_server/r0.6.1#soft-logout
+        #[serde(default, skip_serializing_if = "ruma_serde::is_default")]
+        soft_logout: bool,
+    },
 
     /// M_MISSING_TOKEN
     #[serde(rename = "M_MISSING_TOKEN")]