diff --git a/ironic/drivers/modules/ansible/playbooks/library/facts_wwn.py b/ironic/drivers/modules/ansible/playbooks/library/facts_wwn.py
index f67ce270dc..1656fa7805 100644
--- a/ironic/drivers/modules/ansible/playbooks/library/facts_wwn.py
+++ b/ironic/drivers/modules/ansible/playbooks/library/facts_wwn.py
@@ -41,7 +41,10 @@ def get_devices_wwn(devices, module):
 
         dev_dict[device] = {}
         for key, udev_key in COLLECT_INFO:
-            dev_dict[device][key] = udev.get('ID_%s' % udev_key)
+            candidate = udev.get('ID_%s' % udev_key)
+            if candidate:
+                candidate = candidate.lower()
+            dev_dict[device][key] = candidate
 
     return {"ansible_facts": {"devices_wwn": dev_dict}}
 
diff --git a/ironic/tests/unit/drivers/modules/ansible/test_deploy.py b/ironic/tests/unit/drivers/modules/ansible/test_deploy.py
index 912b4341c6..9978338766 100644
--- a/ironic/tests/unit/drivers/modules/ansible/test_deploy.py
+++ b/ironic/tests/unit/drivers/modules/ansible/test_deploy.py
@@ -345,8 +345,10 @@ class TestAnsibleMethods(AnsibleDeployTestCaseBase):
             ansible_deploy._prepare_extra_vars(host_list, ansible_vars))
 
     def test__parse_root_device_hints(self):
-        hints = {"wwn": "fake wwn", "size": "12345", "rotational": True}
-        expected = {"wwn": "fake wwn", "size": 12345, "rotational": True}
+        hints = {"wwn": "fake wwn", "size": "12345", "rotational": True,
+                 "serial": "HELLO"}
+        expected = {"wwn": "fake wwn", "size": 12345, "rotational": True,
+                    "serial": "hello"}
         props = self.node.properties
         props['root_device'] = hints
         self.node.properties = props
diff --git a/releasenotes/notes/bug-2006275-a5ca234683ca4c32.yaml b/releasenotes/notes/bug-2006275-a5ca234683ca4c32.yaml
new file mode 100644
index 0000000000..94d49b1e84
--- /dev/null
+++ b/releasenotes/notes/bug-2006275-a5ca234683ca4c32.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+    |
+      Fixes an issue with using serial number as root device hints
+      with the ``ansible`` deploy interface.