diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 36c93e7df2..f3a8cbfbd1 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -663,7 +663,7 @@ class Formula
     # special cases to this method.
     if cmd == "python"
       setup_py_in_args = %w[setup.py build.py].include?(args.first)
-      setuptools_shim_in_args = args.any? { |a| a.start_with? "import setuptools" }
+      setuptools_shim_in_args = args.any? { |a| a.to_s.start_with? "import setuptools" }
       if setup_py_in_args || setuptools_shim_in_args
         ENV.refurbish_args
       end