diff --git a/api/client-server/login.yaml b/api/client-server/login.yaml
index ff3eb392..03a1622c 100644
--- a/api/client-server/login.yaml
+++ b/api/client-server/login.yaml
@@ -96,7 +96,6 @@ paths:
             application/json: {
                 "user_id": "@cheeky_monkey:matrix.org",
                 "access_token": "abc123",
-                "home_server": "matrix.org",
                 "device_id": "GHTYAJCE"
               }
           schema:
@@ -112,7 +111,13 @@ paths:
                   This access token can then be used to authorize other requests.
               home_server:
                 type: string
-                description: The hostname of the homeserver on which the account has been registered.
+                description: |-
+                  The server_name of the homeserver on which the account has
+                  been registered.
+
+                  **Deprecated**. Clients should extract the server_name from
+                  ``user_id`` (by splitting at the first colon) if they require
+                  it. Note also that ``homeserver`` is not spelt this way.
               device_id:
                 type: string
                 description: |-
diff --git a/api/client-server/registration.yaml b/api/client-server/registration.yaml
index 52693f5b..fd8f6832 100644
--- a/api/client-server/registration.yaml
+++ b/api/client-server/registration.yaml
@@ -124,7 +124,6 @@ paths:
             application/json: {
                 "user_id": "@cheeky_monkey:matrix.org",
                 "access_token": "abc123",
-                "home_server": "matrix.org",
                 "device_id": "GHTYAJCE"
               }
           schema:
@@ -144,7 +143,13 @@ paths:
                   This access token can then be used to authorize other requests.
               home_server:
                 type: string
-                description: The hostname of the homeserver on which the account has been registered.
+                description: |-
+                  The server_name of the homeserver on which the account has
+                  been registered.
+
+                  **Deprecated**. Clients should extract the server_name from
+                  ``user_id`` (by splitting at the first colon) if they require
+                  it. Note also that ``homeserver`` is not spelt this way.
               device_id:
                 type: string
                 description: |-
diff --git a/changelogs/client_server.rst b/changelogs/client_server.rst
index 13d895fa..8d5f4559 100644
--- a/changelogs/client_server.rst
+++ b/changelogs/client_server.rst
@@ -8,6 +8,12 @@ Unreleased changes
     - ``POST /user_directory/search``
       (`#1096 <https://github.com/matrix-org/matrix-doc/pull/1096>`_).
 
+- Spec clarifications:
+
+  - Mark ``home_server`` return field for ``/login`` and ``/register``
+    endpoints as deprecated
+    (`#1097 <https://github.com/matrix-org/matrix-doc/pull/1097>`_).
+
 r0.3.0
 ======
 
diff --git a/specification/appendices/identifier_grammar.rst b/specification/appendices/identifier_grammar.rst
index d53f61ac..e85bf410 100644
--- a/specification/appendices/identifier_grammar.rst
+++ b/specification/appendices/identifier_grammar.rst
@@ -139,7 +139,7 @@ history includes events with a ``sender`` which does not conform. In order to
 handle these rooms successfully, clients and servers MUST accept user IDs with
 localparts from the expanded character set::
 
-  extended_user_id_char = %x21-7E
+  extended_user_id_char = %x21-39 / %x3B-7F  ; all ascii printing chars except :
 
 Mapping from other character sets
 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<