diff --git a/protocol/json/client.go b/protocol/json/client.go
index 933572b..112ed1d 100644
--- a/protocol/json/client.go
+++ b/protocol/json/client.go
@@ -34,7 +34,7 @@ type clientRequest struct {
 type clientResponse struct {
 	Version string           `json:"jsonrpc"`
 	Result  *json.RawMessage `json:"result"`
-	Error   interface{}      `json:"error"`
+	Error   error            `json:"error"`
 	ID      interface{}      `json:"id"`
 }
 
diff --git a/protocol/json/client_response.go b/protocol/json/client_response.go
index f1398e7..b1d29db 100644
--- a/protocol/json/client_response.go
+++ b/protocol/json/client_response.go
@@ -52,7 +52,7 @@ func (ccr *ClientCodecResponse) Result() interface{} {
 }
 
 func (ccr *ClientCodecResponse) Error() error {
-	return ccr.response.Error.(error)
+	return ccr.response.Error
 }
 
 func (ccr *ClientCodecResponse) Complete() {