diff --git a/Library/Homebrew/dev-cmd/tests.rb b/Library/Homebrew/dev-cmd/tests.rb
index f58fc5d05a..e687b0f6bc 100644
--- a/Library/Homebrew/dev-cmd/tests.rb
+++ b/Library/Homebrew/dev-cmd/tests.rb
@@ -49,7 +49,7 @@ module Homebrew
       ENV["HOMEBREW_TEST_GENERIC_OS"] = "1" if args.generic?
       ENV["HOMEBREW_TEST_ONLINE"] = "1" if args.online?
 
-      ENV["USER"] ||= Utils.popen_read("id", "-nu").chomp
+      ENV["USER"] ||= system_command!("id", args: ["-nu"]).stdout.chomp
 
       # Avoid local configuration messing with tests e.g. git being configured
       # to use GPG to sign by default