diff --git a/src/vim9.h b/src/vim9.h
index f1da323..ddc84b1 100644
--- a/src/vim9.h
+++ b/src/vim9.h
@@ -13,6 +13,7 @@
 
 typedef enum {
     ISN_EXEC,	    // execute Ex command line isn_arg.string
+    ISN_EXECCONCAT, // execute Ex command from isn_arg.number items on stack
     ISN_ECHO,	    // echo isn_arg.echo.echo_count items on top of stack
     ISN_EXECUTE,    // execute Ex commands isn_arg.number items on top of stack
     ISN_ECHOMSG,    // echo Ex commands isn_arg.number items on top of stack