diff --git a/autoload/todo/txt.vim b/autoload/todo/txt.vim
index c5158f0..64a1c46 100644
--- a/autoload/todo/txt.vim
+++ b/autoload/todo/txt.vim
@@ -68,9 +68,17 @@ function! todo#txt#remove_completed()
 
     let l:target_dir = expand('%:p:h')
     let l:todo_file = expand('%:p')
-    let l:done_file = substitute(substitute(l:todo_file, 'todo.txt$', 'done.txt', ''), 'Todo.txt$', 'Done.txt', '')
+    " Check for user-defined g:todo_done_filename
+    if exists("g:todo_done_filename")
+        let l:todo_done_filename = g:todo_done_filename
+    elseif expand('%:t') = 'Todo.txt'
+        let l:todo_done_filename = 'Done.txt'
+    else
+        let l:todo_done_filename = 'done.txt'
+    endif
+    let l:done_file = substitute(substitute(l:todo_file, 'todo.txt$', l:todo_done_filename, ''), 'Todo.txt$', l:todo_done_filename, '')
     if !filewritable(l:done_file) && !filewritable(l:target_dir)
-        echoerr "Can't write to file 'done.txt'"
+        echoerr "Can't write to file '" . l:todo_done_filename . "'"
         return
     endif