diff --git a/autoload/vimwiki/base.vim b/autoload/vimwiki/base.vim
index 16b6384..1086b41 100644
--- a/autoload/vimwiki/base.vim
+++ b/autoload/vimwiki/base.vim
@@ -2143,9 +2143,9 @@ endfunction
 function! vimwiki#base#is_diary_file(filename, ...) abort
   let l:diary_file_paths = a:0 > 0 ? a:1 : vimwiki#diary#get_diary_files()
   let l:normalised_file_paths =
-        \ map(l:diary_file_paths, {_, path -> vimwiki#path#normalize(path)})
+        \ map(l:diary_file_paths, 'vimwiki#path#normalize(v:val)')
   let l:matching_files =
-        \ filter(l:normalised_file_paths, {index, file -> file =~# a:filename})
+        \ filter(l:normalised_file_paths, 'v:val =~# a:filename')
   return len(l:matching_files) > 0 " filename is a diary file if match is found
 endfunction
 
diff --git a/autoload/vimwiki/u.vim b/autoload/vimwiki/u.vim
index e6925fe..d3a2584 100644
--- a/autoload/vimwiki/u.vim
+++ b/autoload/vimwiki/u.vim
@@ -112,7 +112,7 @@ endfunction
 " Sets the filetype to vimwiki
 " If g:vimwiki_filetypes variable is set
 " the filetype will be vimwiki.<ft1>.<ft2> etc.
-function! vimwiki#u#ft_set()
+function! vimwiki#u#ft_set() abort
   let ftypelist = vimwiki#vars#get_global('filetypes')
   let ftype = 'vimwiki'
   for ftypeadd in ftypelist
@@ -125,7 +125,9 @@ endfunction
 " If multiple fileytpes are in use 1 is returned only if the
 " first ft is vimwiki which should always be the case unless
 " the user manually changes it to something else
-function! vimwiki#u#ft_is_vw()
+function! vimwiki#u#ft_is_vw() abort
+  " Clause: is filetype defined
+  if &filetype ==# '' | return 0 | endif
   if split(&filetype, '\.')[0] ==? 'vimwiki'
     return 1
   else