diff --git a/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
index 388fc2c620c0..e0267223887e 100644
--- a/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
+++ b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
@@ -108,7 +108,9 @@ properties:
   riscv,ndev:
     $ref: /schemas/types.yaml#/definitions/uint32
     description:
-      Specifies how many external interrupts are supported by this controller.
+      Specifies how many external (device) interrupts are supported by this
+      controller.  Note that source 0 is reserved in PLIC, so the valid
+      interrupt sources are 1 to riscv,ndev inclusive.
 
   clocks: true