diff --git a/Library/Homebrew/tap.rb b/Library/Homebrew/tap.rb
index b05a1f4fe0..9ea0bcca58 100644
--- a/Library/Homebrew/tap.rb
+++ b/Library/Homebrew/tap.rb
@@ -272,6 +272,7 @@ class Tap
   end
 
   # {TapConfig} of this {Tap}.
+  sig { returns(TapConfig) }
   def config
     @config ||= begin
       raise TapUnavailableError, name unless installed?