diff --git a/protocol/json/client.go b/protocol/json/client.go
index 28c3aab..955656d 100644
--- a/protocol/json/client.go
+++ b/protocol/json/client.go
@@ -35,7 +35,7 @@ type clientResponse struct {
 	Version string           `json:"jsonrpc"`
 	Result  *json.RawMessage `json:"result,omitempty"`
 	Error   error            `json:"error,omitempty"`
-	ID      interface{}      `json:"id"`
+	ID      interface{}      `json:"id,omitempty"`
 }
 
 // clientRequest represents a JSON-RPC request sent by a client.