diff --git a/Library/Homebrew/dev-cmd/livecheck.rb b/Library/Homebrew/dev-cmd/livecheck.rb
index 017f1a9d29..b2ffcbdb16 100644
--- a/Library/Homebrew/dev-cmd/livecheck.rb
+++ b/Library/Homebrew/dev-cmd/livecheck.rb
@@ -1,4 +1,4 @@
-# typed: true
+# typed: strict
 # frozen_string_literal: true
 
 require "abstract_command"
@@ -113,8 +113,9 @@ module Homebrew
 
       private
 
+      sig { returns(String) }
       def watchlist_path
-        @watchlist_path ||= File.expand_path(Homebrew::EnvConfig.livecheck_watchlist)
+        @watchlist_path ||= T.let(File.expand_path(Homebrew::EnvConfig.livecheck_watchlist), T.nilable(String))
       end
     end
   end