diff --git a/Library/Homebrew/dev-cmd/vendor-gems.rb b/Library/Homebrew/dev-cmd/vendor-gems.rb
index 57e42028ae..675136bfe0 100644
--- a/Library/Homebrew/dev-cmd/vendor-gems.rb
+++ b/Library/Homebrew/dev-cmd/vendor-gems.rb
@@ -32,6 +32,9 @@ module Homebrew
 
     ENV["BUNDLE_WITH"] = "sorbet"
 
+    # System Ruby does not pick up the correct SDK by default.
+    ENV["SDKROOT"] = MacOS.sdk_path if ENV["HOMEBREW_MACOS_SYSTEM_RUBY_NEW_ENOUGH"]
+
     ohai "cd #{HOMEBREW_LIBRARY_PATH}"
     HOMEBREW_LIBRARY_PATH.cd do
       if args.update