diff --git a/roles/matrix-bridge-mx-puppet-slack/templates/config.yaml.j2 b/roles/matrix-bridge-mx-puppet-slack/templates/config.yaml.j2
index 5e0b57a19..c7497a84c 100644
--- a/roles/matrix-bridge-mx-puppet-slack/templates/config.yaml.j2
+++ b/roles/matrix-bridge-mx-puppet-slack/templates/config.yaml.j2
@@ -21,7 +21,7 @@ oauth:
   # Slack app credentials.
   # N.B. This must be quoted so YAML does not parse it as a float.
   clientId: '{{ matrix_mx_puppet_slack_oauth_client_id }}'
-  clientSecret: '{{ matrix_mx_puppet_slack_oauth_client_secret }}'
+  clientSecret: {{ matrix_mx_puppet_slack_oauth_client_secret|to_json }}
   # Path where to listen for OAuth redirect callbacks.
   redirectPath: {{ matrix_mx_puppet_slack_redirect_path }}
   # Set up proxying from https://your.domain/redirect_path to http://bindAddress:port/redirect_path,