diff --git a/octavia/api/v2/controllers/health_monitor.py b/octavia/api/v2/controllers/health_monitor.py
index 2c8782e954..a1d0a01289 100644
--- a/octavia/api/v2/controllers/health_monitor.py
+++ b/octavia/api/v2/controllers/health_monitor.py
@@ -188,7 +188,9 @@ class HealthMonitorController(base.BaseController):
             request.type == consts.HEALTH_MONITOR_UDP_CONNECT)
         conf_min_delay = (
             CONF.api_settings.udp_connect_min_interval_health_monitor)
-        if hm_is_type_udp and request.delay < conf_min_delay:
+        if (hm_is_type_udp and
+                not isinstance(request.delay, wtypes.UnsetType) and
+                request.delay < conf_min_delay):
             raise exceptions.ValidationException(detail=_(
                 "The request delay value %(delay)s should be larger than "
                 "%(conf_min_delay)s for %(type)s health monitor type.") % {
diff --git a/octavia/tests/functional/api/v2/test_health_monitor.py b/octavia/tests/functional/api/v2/test_health_monitor.py
index 62633dfba6..68a662d9f8 100644
--- a/octavia/tests/functional/api/v2/test_health_monitor.py
+++ b/octavia/tests/functional/api/v2/test_health_monitor.py
@@ -1782,6 +1782,24 @@ class TestHealthMonitor(base.BaseAPITest):
             pool_prov_status=constants.PENDING_UPDATE,
             hm_prov_status=constants.PENDING_UPDATE)
 
+    def test_update_udp_case_with_udp_hm(self):
+        api_hm = self.create_health_monitor(
+            self.udp_pool_with_listener_id,
+            constants.HEALTH_MONITOR_UDP_CONNECT, 3, 1, 1, 1).get(
+            self.root_tag)
+        self.set_lb_status(self.udp_lb_id)
+        new_hm = {'timeout': 2}
+        self.put(
+            self.HM_PATH.format(healthmonitor_id=api_hm.get('id')),
+            self._build_body(new_hm))
+        self.assert_correct_status(
+            lb_id=self.udp_lb_id, listener_id=self.udp_listener_id,
+            pool_id=self.udp_pool_with_listener_id, hm_id=api_hm.get('id'),
+            lb_prov_status=constants.PENDING_UPDATE,
+            listener_prov_status=constants.PENDING_UPDATE,
+            pool_prov_status=constants.PENDING_UPDATE,
+            hm_prov_status=constants.PENDING_UPDATE)
+
     def test_negative_update_udp_case(self):
         api_hm = self.create_health_monitor(
             self.udp_pool_with_listener_id,
diff --git a/releasenotes/notes/Fix-UDP-Health-monitor-update-without-delay-c56240e59e15483f.yaml b/releasenotes/notes/Fix-UDP-Health-monitor-update-without-delay-c56240e59e15483f.yaml
new file mode 100644
index 0000000000..40c7450492
--- /dev/null
+++ b/releasenotes/notes/Fix-UDP-Health-monitor-update-without-delay-c56240e59e15483f.yaml
@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fixed error on update UDP Health Monitor with empty "delay" parameter