diff --git a/Library/Homebrew/formula_assertions.rb b/Library/Homebrew/formula_assertions.rb
index a1741f6658..f0562fe33a 100644
--- a/Library/Homebrew/formula_assertions.rb
+++ b/Library/Homebrew/formula_assertions.rb
@@ -36,7 +36,7 @@ module Homebrew
     # optionally asserts the exit status.
     #
     # @api public
-    sig { params(cmd: String, input: T.nilable(String), result: T.nilable(Integer)).returns(String) }
+    sig { params(cmd: T.any(String, Pathname), input: T.nilable(String), result: T.nilable(Integer)).returns(String) }
     def pipe_output(cmd, input = nil, result = nil)
       ohai cmd
       output = IO.popen(cmd, "w+") do |pipe|