diff --git a/plugin/obsession.vim b/plugin/obsession.vim
index e36729d..ef2a998 100644
--- a/plugin/obsession.vim
+++ b/plugin/obsession.vim
@@ -75,8 +75,13 @@ function! s:persist() abort
       execute 'mksession!' fnameescape(tmp)
       let v:this_session = g:this_obsession
       let body = readfile(tmp)
-      call insert(body, 'let g:this_session = v:this_session', -3)
-      call insert(body, 'let g:this_obsession = v:this_session', -3)
+      if body[0] ==# 'vim9script'
+          call insert(body, 'g:this_session = v:this_session', -3)
+          call insert(body, 'g:this_obsession = v:this_session', -3)
+      else
+          call insert(body, 'let g:this_session = v:this_session', -3)
+          call insert(body, 'let g:this_obsession = v:this_session', -3)
+      endif
       if type(get(g:, 'obsession_append')) == type([])
         for line in g:obsession_append
           call insert(body, line, -3)