diff --git a/openapi.yaml b/openapi.yaml
index 490b989d..c3bbdc6b 100644
--- a/openapi.yaml
+++ b/openapi.yaml
@@ -128,6 +128,7 @@ components:
           description: Hex-encoded libp2p public key of the node
         mixPubKey:
           type: string
+          nullable: true
           description: Hex-encoded mix public key (present only for nodes that support mix)
         table:
           $ref: "#/components/schemas/PeersTable"