diff --git a/roles/mailman3/templates/mailman.cfg.j2 b/roles/mailman3/templates/mailman.cfg.j2
index c234177ca2..c64e35727c 100644
--- a/roles/mailman3/templates/mailman.cfg.j2
+++ b/roles/mailman3/templates/mailman.cfg.j2
@@ -81,7 +81,7 @@ jump_chain: discard
 
 [mta]
 # Email is sent on the submission port to bypass spam checking.
-smtp_port: { mailman_smtp_port }
+smtp_port: {{ mailman_smtp_port }}
 # Remove DKIM signatures in the email headers.
 remove_dkim_headers: yes
 # Don't process old stale bounces