diff --git a/autoload/vimwiki/diary.vim b/autoload/vimwiki/diary.vim
index c55b3eb..1ceeb2e 100644
--- a/autoload/vimwiki/diary.vim
+++ b/autoload/vimwiki/diary.vim
@@ -176,6 +176,9 @@ endfunction
 function! vimwiki#diary#make_note(wnum, ...)
   if a:wnum == 0
     let wiki_nr = vimwiki#vars#get_bufferlocal('wiki_nr')
+    if wiki_nr < 0  " this happens when e.g. VimwikiMakeDiaryNote was called outside a wiki buffer
+      let wiki_nr = 0
+    endif
   else
     let wiki_nr = a:wnum - 1
   endif