diff --git a/sex-mode.el b/sex-mode.el
index 99434c2..8eb676e 100644
--- a/sex-mode.el
+++ b/sex-mode.el
@@ -80,6 +80,7 @@ All commands in `lisp-mode-shared-map' are inherited by this map.")
 (put 'pub 'lisp-indent-function 'defun)
 (put 'defmacro 'lisp-indent-function 'defun)
 (put 'struct 'lisp-indent-function 'defun)
+(put 'union 'lisp-indent-function 'defun)
 (put 'var 'lisp-indent-function 0)
 (put 'import 'lisp-indent-function 1)