diff --git a/demo-json-rpc-server.c b/demo-json-rpc-server.c
index cf4d374..6ae1742 100644
--- a/demo-json-rpc-server.c
+++ b/demo-json-rpc-server.c
@@ -711,7 +711,7 @@ ws_handler_on_frame (void *user_data, const struct ws_parser *parser)
 		return true;
 
 	if (self->message_opcode == WS_OPCODE_TEXT
-	 && !utf8_validate (self->parser.input.str, self->parser.input.len))
+	 && !utf8_validate (self->message_data.str, self->message_data.len))
 	{
 		ws_handler_fail (self, WS_STATUS_INVALID_PAYLOAD_DATA);
 		return false;