diff --git a/lib/elixlsx/sheet.ex b/lib/elixlsx/sheet.ex
index 40cddd2..dcf70bc 100644
--- a/lib/elixlsx/sheet.ex
+++ b/lib/elixlsx/sheet.ex
@@ -222,7 +222,7 @@ defmodule Elixlsx.Sheet do
     %{sheet | pane_freeze: nil}
   end
 
-  @spec add_data_validations(Sheet.t(), String.t(), String.t(), list(String.t())) :: Sheet.t()
+  @spec add_data_validations(Sheet.t(), String.t(), String.t(), String.t() | list(String.t())) :: Sheet.t()
   def add_data_validations(sheet, start_cell, end_cell, values) do
     %{sheet | data_validations: [{start_cell, end_cell, values} | sheet.data_validations]}
   end