diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index f1123f9246..e168965158 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -1566,7 +1566,7 @@ class Formula
   sig {
     params(
       install_prefix: T.any(String, Pathname),
-      install_libdir: String,
+      install_libdir: T.any(String, Pathname),
       find_framework: String,
     ).returns(T::Array[String])
   }