diff --git a/changelog.d/5478.misc b/changelog.d/5478.misc
new file mode 100644
index 0000000000..829bb1e521
--- /dev/null
+++ b/changelog.d/5478.misc
@@ -0,0 +1 @@
+The demo servers talk to each other again.
diff --git a/demo/README b/demo/README
index 0b584ceb15..0bec820ad6 100644
--- a/demo/README
+++ b/demo/README
@@ -1,9 +1,13 @@
+DO NOT USE THESE DEMO SERVERS IN PRODUCTION
+
 Requires you to have done:
     python setup.py develop
 
 
-The demo start.sh will start three synapse servers on ports 8080, 8081 and 8082, with host names localhost:$port. This can be easily changed to `hostname`:$port in start.sh if required. 
-It will also start a web server on port 8000 pointed at the webclient.
+The demo start.sh will start three synapse servers on ports 8080, 8081 and 8082, with host names localhost:$port. This can be easily changed to `hostname`:$port in start.sh if required.
+
+To enable the servers to communicate untrusted ssl certs are used. In order to do this the servers do not check the certs
+and are configured in a highly insecure way. Do not use these configuration files in production.
 
 stop.sh will stop the synapse servers and the webclient.
 
diff --git a/demo/start.sh b/demo/start.sh
index 5c3a8fe61f..1c4f12d0bb 100755
--- a/demo/start.sh
+++ b/demo/start.sh
@@ -27,8 +27,70 @@ for port in 8080 8081 8082; do
         --config-path "$DIR/etc/$port.config" \
         --report-stats no
 
-    printf '\n\n# Customisation made by demo/start.sh\n' >> $DIR/etc/$port.config
-    echo 'enable_registration: true' >> $DIR/etc/$port.config
+    if ! grep -F "Customisation made by demo/start.sh" -q  $DIR/etc/$port.config; then
+        printf '\n\n# Customisation made by demo/start.sh\n' >> $DIR/etc/$port.config
+        
+        echo 'enable_registration: true' >> $DIR/etc/$port.config
+
+        # Warning, this heredoc depends on the interaction of tabs and spaces. Please don't
+        # accidentaly bork me with your fancy settings.
+		listeners=$(cat <<-PORTLISTENERS
+		# Configure server to listen on both $https_port and $port
+		# This overides some of the default settings above
+		listeners:
+		  - port: $https_port
+		    type: http
+		    tls: true
+		    resources:
+		      - names: [client, federation]
+		
+		  - port: $port
+		    tls: false
+		    bind_addresses: ['::1', '127.0.0.1']
+		    type: http
+		    x_forwarded: true
+		    resources:
+		      - names: [client, federation]
+		        compress: false
+		PORTLISTENERS
+		)
+        echo "${listeners}" >> $DIR/etc/$port.config
+
+        # Disable tls for the servers
+        printf '\n\n# Disable tls on the servers.' >> $DIR/etc/$port.config
+        echo '# DO NOT USE IN PRODUCTION' >> $DIR/etc/$port.config
+        echo 'use_insecure_ssl_client_just_for_testing_do_not_use: true' >> $DIR/etc/$port.config
+        echo 'federation_verify_certificates: false' >> $DIR/etc/$port.config
+
+        # Set tls paths
+        echo "tls_certificate_path: \"$DIR/etc/localhost:$https_port.tls.crt\"" >> $DIR/etc/$port.config
+        echo "tls_private_key_path: \"$DIR/etc/localhost:$https_port.tls.key\"" >> $DIR/etc/$port.config
+
+        # Generate tls keys
+        openssl req -x509 -newkey rsa:4096 -keyout $DIR/etc/localhost\:$https_port.tls.key -out $DIR/etc/localhost\:$https_port.tls.crt -days 365 -nodes -subj "/O=matrix"
+        
+        # Ignore keys from the trusted keys server
+        echo '# Ignore keys from the trusted keys server' >> $DIR/etc/$port.config
+        echo 'trusted_key_servers:' >> $DIR/etc/$port.config
+        echo '  - server_name: "matrix.org"' >> $DIR/etc/$port.config
+        echo '    accept_keys_insecurely: true' >> $DIR/etc/$port.config
+
+        # Reduce the blacklist
+        blacklist=$(cat <<-BLACK
+		# Set the blacklist so that it doesn't include 127.0.0.1
+		federation_ip_range_blacklist:
+		  - '10.0.0.0/8'
+		  - '172.16.0.0/12'
+		  - '192.168.0.0/16'
+		  - '100.64.0.0/10'
+		  - '169.254.0.0/16'
+		  - '::1/128'
+		  - 'fe80::/64'
+		  - 'fc00::/7'
+		BLACK
+		)
+        echo "${blacklist}" >> $DIR/etc/$port.config
+    fi
 
     # Check script parameters
     if [ $# -eq 1 ]; then