diff --git a/Documentation/devicetree/bindings/mailbox/fsl,mu.yaml b/Documentation/devicetree/bindings/mailbox/fsl,mu.yaml
index 7ed096360be2..15cef82cd356 100644
--- a/Documentation/devicetree/bindings/mailbox/fsl,mu.yaml
+++ b/Documentation/devicetree/bindings/mailbox/fsl,mu.yaml
@@ -72,6 +72,9 @@ properties:
     description: boolean, if present, means it is for side B MU.
     type: boolean
 
+  power-domains:
+    maxItems: 1
+
 required:
   - compatible
   - reg