diff --git a/changelogs/server_server/newsfragments/1559.clarification b/changelogs/server_server/newsfragments/1559.clarification
new file mode 100644
index 00000000..401a94e0
--- /dev/null
+++ b/changelogs/server_server/newsfragments/1559.clarification
@@ -0,0 +1 @@
+Fix definition of response of `POST /_matrix/federation/v1/user/keys/claim`.
diff --git a/data/api/server-server/user_keys.yaml b/data/api/server-server/user_keys.yaml
index 60995a74..fb598e94 100644
--- a/data/api/server-server/user_keys.yaml
+++ b/data/api/server-server/user_keys.yaml
@@ -71,26 +71,28 @@ paths:
                         type: object
                         # Key
                         additionalProperties:
-                          type: object
-                          title: KeyObject
-                          properties:
-                            key:
-                              type: string
-                              description: The key, encoded using unpadded base64.
-                            signatures:
-                              type: object
-                              title: Signatures
-                              additionalProperties:
-                                type: object
-                                additionalProperties:
+                          oneOf:
+                            - type: string
+                            - type: object
+                              title: KeyObject
+                              properties:
+                                key:
                                   type: string
-                              description: |-
-                                Signature of the key object.
+                                  description: The key, encoded using unpadded base64.
+                                signatures:
+                                  type: object
+                                  title: Signatures
+                                  additionalProperties:
+                                    type: object
+                                    additionalProperties:
+                                      type: string
+                                  description: |-
+                                    Signature of the key object.
 
-                                The signature is calculated using the process described at [Signing JSON](/appendices/#signing-json).
-                          required:
-                            - key
-                            - signatures
+                                    The signature is calculated using the process described at [Signing JSON](/appendices/#signing-json).
+                              required:
+                                - key
+                                - signatures
                     example:
                       "@alice:example.com":
                         JLAFKJWSCS:
diff --git a/layouts/partials/json-schema/resolve-additional-types.html b/layouts/partials/json-schema/resolve-additional-types.html
index 58710076..449b4222 100644
--- a/layouts/partials/json-schema/resolve-additional-types.html
+++ b/layouts/partials/json-schema/resolve-additional-types.html
@@ -91,6 +91,21 @@
     {{ end }}
 {{ end }}
 
+{{/*
+  Handle object schemas using the `oneOf` keyword
+  (https://json-schema.org/understanding-json-schema/reference/combining.html#oneof)
+*/}}
+{{ if $this_object.oneOf }}
+    {{ range $idx, $item := $this_object.oneOf }}
+        {{ $additional_objects = partial "get-additional-objects" (dict
+            "this_object" $item
+            "additional_objects" $additional_objects
+            "anchor_base" $anchor_base
+            "name" (printf "%s.oneOf[%d]" $name $idx)
+        ) }}
+    {{ end }}
+{{ end }}
+
 {{ return $additional_objects }}
 
 
diff --git a/layouts/partials/openapi/render-object-table.html b/layouts/partials/openapi/render-object-table.html
index 4fc5ac76..0f5841a4 100644
--- a/layouts/partials/openapi/render-object-table.html
+++ b/layouts/partials/openapi/render-object-table.html
@@ -36,7 +36,7 @@
         {{ $property := partial "json-schema/resolve-allof" $property }}
         {{ $type := $property.type }}
 
-        {{ if eq $property.type "object" }}
+        {{ if or (eq $property.type "object") (and $property.oneOf (reflect.IsSlice .oneOf)) }}
             {{ $type = partial "type-or-title" $property }}
         {{ end }}
 
@@ -121,7 +121,7 @@
         {{ $types := slice }}
 
         {{ range .oneOf }}
-            {{ $types = $types | append .type }}
+            {{ $types = $types | append (partial "type-or-title" .) }}
         {{ end }}
 
         {{ $type = delimit $types "|" }}