diff --git a/draft-ietf-httpbis-origin-frame.md b/draft-ietf-httpbis-origin-frame.md
index 0b4ca3cdb..96771f76c 100644
--- a/draft-ietf-httpbis-origin-frame.md
+++ b/draft-ietf-httpbis-origin-frame.md
@@ -39,10 +39,10 @@ given connection.
 
 --- note_Note_to_Readers
 
-Discussion of this draft takes place on the HTTP working group mailing list 
+Discussion of this draft takes place on the HTTP working group mailing list
 (ietf-http-wg@w3.org), which is archived at <https://lists.w3.org/Archives/Public/ietf-http-wg/>.
 
-Working Group information can be found at <http://httpwg.github.io/>; source 
+Working Group information can be found at <http://httpwg.github.io/>; source
 code and issues list for this draft can be found at <https://github.com/httpwg/http-extensions/labels/origin-frame>.
 
 --- middle
@@ -144,12 +144,12 @@ See {{algo}} for an illustrative algorithm for processing ORIGIN frames.
 The set of origins (as per {{!RFC6454}}) that a given connection might be used for is known in this
 specification as the Origin Set.
 
-By default, a connection's Origin Set is uninitialised. When an ORIGIN frame is first received and
-successfully processed by a client, the connection's Origin Set is defined to contain a single
-origin, composed from:
+By default, the Origin Set for a connection is uninitialised. When an ORIGIN frame is first received
+and successfully processed by a client, the connection's Origin Set is defined to contain an initial
+origin.  The initial origin is composed from:
 
   - Scheme: "https"
-  - Host: the value sent in Server Name Indication ({{!RFC6066}} Section 3), converted to lower case
+  - Host: the value sent in Server Name Indication (SNI, {{!RFC6066}} Section 3), converted to lower case
   - Port: the remote port of the connection (i.e., the server's port)
 
 The contents of that ORIGIN frame (and subsequent ones) allows the server to incrementally add new
@@ -160,6 +160,22 @@ The Origin Set is also affected by the 421 (Misdirected Request) response status
 MUST create the ASCII serialisation of the corresponding request's origin (as per {{!RFC6454}},
 Section 6.2) and remove it from the connection's Origin Set, if present.
 
+Note:
+
+: When sending an ORIGIN frame to a connection that is initialised as an Alternative Service
+  {{?RFC7838}}, the initial origin set {{set}} will contain an origin with the appropriate
+  scheme and hostname (since Alternative Services specifies that the origin's hostname be sent
+  in SNI). However, it is possible that the port will be different than that of the intended
+  origin, since the initial origin set is calculated using the actual port in use, which can be
+  different for the alternative service. In this case, the intended origin needs to be sent in
+  the ORIGIN frame explicitly.
+
+: For example, a client making requests for "https://example.com" is directed to an alternative
+  service at ("h2", "x.example.net", "8443").  If this alternative service sends an ORIGIN
+  frame, the initial origin will be "https://example.com:8443".  The client will not be able to
+  use the alternative service to make requests for "https://example.com" unless that origin is
+  explicitly included in the ORIGIN frame.
+
 
 ## Authority, Push and Coalescing with ORIGIN {#authority}
 
@@ -190,6 +206,9 @@ that a client might have more than one viable connection to an origin open at an
 occurs, clients SHOULD not emit new requests on any connection whose Origin Set is a proper subset
 of another connection's Origin Set, and SHOULD close it once all outstanding requests are satisfied.
 
+The Origin Set is unaffected by any alternative services {{?RFC7838}} advertisements made by the
+server.  Advertising an alternative service does not affect whether a server is authoritative.
+
 
 # IANA Considerations