diff --git a/gunicorn.conf.py b/gunicorn.conf.py
index 09ca796..2e84f65 100644
--- a/gunicorn.conf.py
+++ b/gunicorn.conf.py
@@ -1,7 +1,9 @@
 """Gunicorn settings; each can be overridden with GUNICORN_* env vars."""
 import os
 
-bind = os.environ.get("GUNICORN_BIND", "0.0.0.0:8000")
+# [::] is dual-stack on Linux: it accepts IPv6 and IPv4. 0.0.0.0 would be
+# IPv4 only and unreachable on IPv6-only clusters.
+bind = os.environ.get("GUNICORN_BIND", "[::]:8000")
 # Threaded workers: requests mostly wait on LDAP, SMTP and the OTP server.
 worker_class = "gthread"
 workers = int(os.environ.get("GUNICORN_WORKERS", "2"))