diff --git a/group_vars/matrix_servers b/group_vars/matrix_servers
index 192d43383..5efde0c95 100755
--- a/group_vars/matrix_servers
+++ b/group_vars/matrix_servers
@@ -106,7 +106,7 @@ matrix_appservice_slack_enabled: false
 # Normally, matrix-nginx-proxy is enabled and nginx can reach matrix-appservice-slack over the container network.
 # If matrix-nginx-proxy is not enabled, or you otherwise have a need for it, you can expose
 # matrix-appservice-slack's client-server port to the local host.
-matrix_appservice_slack_container_http_host_bind_port: "{{ '' if matrix_nginx_proxy_enabled else '127.0.0.1:{{ matrix_appservice_slack_slack_port }}' }}"
+matrix_appservice_slack_container_http_host_bind_port: "{{ '' if matrix_nginx_proxy_enabled else ('127.0.0.1:' ~ matrix_appservice_slack_slack_port) }}"
 
 matrix_appservice_slack_appservice_token: "{{ matrix_synapse_macaroon_secret_key | password_hash('sha512', 'slack.as.token') | to_uuid }}"