diff --git a/changelogs/server_server/newsfragments/1672.clarification b/changelogs/server_server/newsfragments/1672.clarification
new file mode 100644
index 00000000..d664c0b3
--- /dev/null
+++ b/changelogs/server_server/newsfragments/1672.clarification
@@ -0,0 +1 @@
+Clarify that federation requests for non-local users are invalid.
diff --git a/data/api/server-server/query.yaml b/data/api/server-server/query.yaml
index 23a6dffd..8d727a57 100644
--- a/data/api/server-server/query.yaml
+++ b/data/api/server-server/query.yaml
@@ -121,7 +121,7 @@ paths:
       parameters:
         - in: query
           name: user_id
-          description: The user ID to query.
+          description: The user ID to query. Must be a user local to the receiving homeserver.
           required: true
           example: "@someone:example.org"
           schema:
diff --git a/data/api/server-server/user_keys.yaml b/data/api/server-server/user_keys.yaml
index fb598e94..be50fcea 100644
--- a/data/api/server-server/user_keys.yaml
+++ b/data/api/server-server/user_keys.yaml
@@ -34,7 +34,8 @@ paths:
                   type: object
                   description: |-
                     The keys to be claimed. A map from user ID, to a map from
-                    device ID to algorithm name.
+                    device ID to algorithm name. Requested users must be local
+                    to the receiving homeserver.
                   additionalProperties:
                     type: object
                     additionalProperties:
@@ -121,7 +122,8 @@ paths:
                   description: |-
                     The keys to be downloaded. A map from user ID, to a list of
                     device IDs, or to an empty list to indicate all devices for the
-                    corresponding user.
+                    corresponding user.  Requested users must be local to the
+                    receiving homeserver.
                   additionalProperties:
                     type: array
                     items: