diff --git a/rpc/handler.go b/rpc/handler.go
index c8571ad795..23023eaca1 100644
--- a/rpc/handler.go
+++ b/rpc/handler.go
@@ -296,10 +296,16 @@ func (h *handler) handleCallMsg(ctx *callProc, msg *jsonrpcMessage) *jsonrpcMess
 		return nil
 	case msg.isCall():
 		resp := h.handleCall(ctx, msg)
+		var ctx []interface{}
+		ctx = append(ctx, "reqid", idForLog{msg.ID}, "t", time.Since(start))
 		if resp.Error != nil {
-			h.log.Warn("Served "+msg.Method, "reqid", idForLog{msg.ID}, "t", time.Since(start), "err", resp.Error.Message)
+			ctx = append(ctx, "err", resp.Error.Message)
+			if resp.Error.Data != nil {
+				ctx = append(ctx, "errdata", resp.Error.Data)
+			}
+			h.log.Warn("Served "+msg.Method, ctx...)
 		} else {
-			h.log.Debug("Served "+msg.Method, "reqid", idForLog{msg.ID}, "t", time.Since(start))
+			h.log.Debug("Served "+msg.Method, ctx...)
 		}
 		return resp
 	case msg.hasValidID():
diff --git a/rpc/json.go b/rpc/json.go
index 5b48e01e67..3be5d55f48 100644
--- a/rpc/json.go
+++ b/rpc/json.go
@@ -139,6 +139,10 @@ func (err *jsonError) ErrorCode() int {
 	return err.Code
 }
 
+func (err *jsonError) ErrorData() interface{} {
+	return err.Data
+}
+
 // Conn is a subset of the methods of net.Conn which are sufficient for ServerCodec.
 type Conn interface {
 	io.ReadWriteCloser