diff --git a/ironic/api/controllers/v1/node.py b/ironic/api/controllers/v1/node.py
index cba7a4e5cc..46c02521d4 100644
--- a/ironic/api/controllers/v1/node.py
+++ b/ironic/api/controllers/v1/node.py
@@ -1988,6 +1988,9 @@ class NodesController(rest.RestController):
             # of just before saving so we calculate correctly.
             if field == 'conductor_group':
                 patch_val = patch_val.lower()
+            # Node object protected field is not nullable
+            if field == 'protected' and patch_val is None:
+                patch_val = False
             if rpc_node[field] != patch_val:
                 rpc_node[field] = patch_val
 
diff --git a/releasenotes/notes/protected-unset-0620b844afbb635e.yaml b/releasenotes/notes/protected-unset-0620b844afbb635e.yaml
new file mode 100644
index 0000000000..f516a5c0e2
--- /dev/null
+++ b/releasenotes/notes/protected-unset-0620b844afbb635e.yaml
@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fixes HTTP 500 when trying to unset the ``protected`` attribute via
+    the CLI.