diff --git a/changelog.d/12783.misc b/changelog.d/12783.misc
new file mode 100644
index 000000000000..97575608bb8b
--- /dev/null
+++ b/changelog.d/12783.misc
@@ -0,0 +1 @@
+Fix federation when using the demo scripts.
diff --git a/demo/start.sh b/demo/start.sh
index 5a9972d24c2c..96b3a2ceab2f 100755
--- a/demo/start.sh
+++ b/demo/start.sh
@@ -12,6 +12,7 @@ export PYTHONPATH
 
 echo "$PYTHONPATH"
 
+# Create servers which listen on HTTP at 808x and HTTPS at 848x.
 for port in 8080 8081 8082; do
     echo "Starting server on port $port... "
 
@@ -19,10 +20,12 @@ for port in 8080 8081 8082; do
     mkdir -p demo/$port
     pushd demo/$port || exit
 
-    # Generate the configuration for the homeserver at localhost:848x.
+    # Generate the configuration for the homeserver at localhost:848x, note that
+    # the homeserver name needs to match the HTTPS listening port for federation
+    # to properly work..
     python3 -m synapse.app.homeserver \
         --generate-config \
-        --server-name "localhost:$port" \
+        --server-name "localhost:$https_port" \
         --config-path "$port.config" \
         --report-stats no
 
diff --git a/docs/development/demo.md b/docs/development/demo.md
index 4277252ceb60..893ed6998ebb 100644
--- a/docs/development/demo.md
+++ b/docs/development/demo.md
@@ -5,7 +5,7 @@
 Requires you to have a [Synapse development environment setup](https://matrix-org.github.io/synapse/develop/development/contributing_guide.html#4-install-the-dependencies).
 
 The demo setup allows running three federation Synapse servers, with server
-names `localhost:8080`, `localhost:8081`, and `localhost:8082`.
+names `localhost:8480`, `localhost:8481`, and `localhost:8482`.
 
 You can access them via any Matrix client over HTTP at `localhost:8080`,
 `localhost:8081`, and `localhost:8082` or over HTTPS at `localhost:8480`,
@@ -20,9 +20,10 @@ and the servers are configured in a highly insecure way, including:
 The servers are configured to store their data under `demo/8080`, `demo/8081`, and
 `demo/8082`. This includes configuration, logs, SQLite databases, and media.
 
-Note that when joining a public room on a different HS via "#foo:bar.net", then
-you are (in the current impl) joining a room with room_id "foo". This means that
-it won't work if your HS already has a room with that name.
+Note that when joining a public room on a different homeserver via "#foo:bar.net",
+then you are (in the current implementation) joining a room with room_id "foo".
+This means that it won't work if your homeserver already has a room with that
+name.
 
 ## Using the demo scripts