diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index 5bad532b3b..fa388237cc 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -271,6 +271,7 @@ class Tap
   end
 
   # {TapConfig} of this {Tap}.
+  sig { returns(TapConfig) }
   def config
     @config ||= begin
       raise TapUnavailableError, name unless installed?