diff --git a/ansible/group_vars/all.yml b/ansible/group_vars/all.yml
index 5ec9f5da89..c7a2414aae 100644
--- a/ansible/group_vars/all.yml
+++ b/ansible/group_vars/all.yml
@@ -573,6 +573,7 @@ placement_api_public_port: "{{ haproxy_single_external_frontend_public_port if h
 prometheus_external_fqdn: "{{ kolla_external_fqdn }}"
 prometheus_internal_fqdn: "{{ kolla_internal_fqdn }}"
 prometheus_port: "9091"
+prometheus_listen_port: "{{ prometheus_port }}"
 prometheus_public_port: "{{ haproxy_single_external_frontend_public_port if haproxy_single_external_frontend | bool else prometheus_port }}"
 prometheus_node_exporter_port: "9100"
 prometheus_mysqld_exporter_port: "9104"
diff --git a/ansible/roles/prometheus/defaults/main.yml b/ansible/roles/prometheus/defaults/main.yml
index ae5d7292b3..e66d0d44da 100644
--- a/ansible/roles/prometheus/defaults/main.yml
+++ b/ansible/roles/prometheus/defaults/main.yml
@@ -18,7 +18,9 @@ prometheus_services:
         enabled: "{{ enable_prometheus_server_external | bool }}"
         mode: "http"
         external: true
+        external_fqdn: "{{ prometheus_external_fqdn }}"
         port: "{{ prometheus_public_port }}"
+        listen_port: "{{ prometheus_listen_port }}"
         active_passive: "{{ prometheus_active_passive | bool }}"
   prometheus-node-exporter:
     container_name: prometheus_node_exporter
diff --git a/releasenotes/notes/fix-expose-prometheus-externally-with-single-frontend-45ca4e25c8948393.yaml b/releasenotes/notes/fix-expose-prometheus-externally-with-single-frontend-45ca4e25c8948393.yaml
new file mode 100644
index 0000000000..b720e60ed5
--- /dev/null
+++ b/releasenotes/notes/fix-expose-prometheus-externally-with-single-frontend-45ca4e25c8948393.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes an issue when using ``enable_prometheus_server_external`` in
+    conjunction with ``haproxy_single_external_frontend``.