diff --git a/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2 b/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2
index c51a60a0..9e7777fd 100644
--- a/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2
+++ b/roles/matrix-synapse/templates/synapse/homeserver.yaml.j2
@@ -893,7 +893,7 @@ report_stats: {{ matrix_synapse_report_stats|to_json }}
 
 # A list of application service config files to use
 #
-app_service_config_files: {{ matrix_synapse_app_service_config_files }}
+app_service_config_files: {{ matrix_synapse_app_service_config_files|to_json }}
 
 # Uncomment to enable tracking of application service IP addresses. Implicitly
 # enables MAU tracking for application service users.