diff --git a/lua/harpoon/mark.lua b/lua/harpoon/mark.lua
index 8ce8a47..3b6543c 100644
--- a/lua/harpoon/mark.lua
+++ b/lua/harpoon/mark.lua
@@ -74,14 +74,19 @@ local function swap(a_idx, b_idx)
     config.marks[b_idx] = tmp
 end
 
-M.add_file = function()
-    local buf_name = get_buf_name()
+M.add_file = function(file_name_or_buf_id)
+    local buf_name = get_buf_name(file_name_or_buf_id)
 
     if valid_index(get_index_of(buf_name)) then
         -- we don't alter file layout.
         return
     end
 
+    if buf_name == "" or buf_name == nil then
+        error("Couldn't find a valid file name to mark, sorry.")
+        return
+    end
+
     local config = harpoon.get_mark_config()
     for idx = 1, #config.marks do
         if config.marks[idx] == nil then