diff --git a/pkgs/net-pkgs/net-doc/net/scribblings/git-checkout.scrbl b/pkgs/net-pkgs/net-doc/net/scribblings/git-checkout.scrbl
index ab05a3c113..1c6beee09f 100644
--- a/pkgs/net-pkgs/net-doc/net/scribblings/git-checkout.scrbl
+++ b/pkgs/net-pkgs/net-doc/net/scribblings/git-checkout.scrbl
@@ -7,7 +7,9 @@
 @defmodule[net/git-checkout]{The @racketmodname[net/git-checkout]
 library provides support for extracting a directory tree from a Git
 repository that is hosted by a server that implements the @tt{git://}
-protocol or the ``smart'' protocol over HTTP(S). The
+protocol or the ``smart'' protocol over HTTP(S).@margin-note*{The
+``dumb'' protocol over HTTP(S) is supported for reference discovery,
+but not for obtaining repository content.} The
 @racketmodname[net/git-checkout] library does not rely on external
 binaries (such as a @exec{git} client) or Git-specific native
 libraries (such as @filepath{libgit}).}
@@ -31,13 +33,14 @@ for information on command-line arguments and flags.
                        [#:tmp-dir given-tmp-dir (or/c #f path-string?) #f]
                        [#:clean-tmp-dir? clean-tmp-dir? any/c (not given-tmp-dir)]
                        [#:verify-server? verify-server? any/c #t]
-                       [#:port port (integer-in 1 65535) (case transport
-                                                           [(git) 9418]
-                                                           [(http) 80]
-                                                           [(https) 443])])
+                       [#:port port (or/c #f (integer-in 1 65535)) (case transport
+                                                                     [(git) 9418]
+                                                                     [(http) 80]
+                                                                     [(https) 443])])
          string?]{
 
 Contacts the server at @racket[hostname] and @racket[port]
+(where @racket[#f] is replaced by the default)
 to download the repository whose name on the server is
 @racket[repository] (normally ending in @filepath{.git}).  The tree
 within the repository that is identified by @racket[ref] (which can be
@@ -47,7 +50,9 @@ a branch, tag, commit ID, or tree ID) is extracted to
 If @racket[transport] is @racket['git], then the server is contacted
 using Git's native transport. If @racket[transport] is
 @racket['http] or @racket['https], then the server is contacted using
-HTTP(S) and the ``smart'' Git protocol. In the case of @racket['https],
+HTTP(S) and the ``smart'' Git protocol; if the server supports only
+the ``dumb'' protocol, then @racket[dest-dir] must be @racket[#f].  In
+the case of @racket['https],
 the server's identity is verified unless @racket[verify-server?] is
 false or the @indexed-envvar{GIT_SSL_NO_VERIFY} environment variable
 is set.