diff --git a/tools/test-environment.lisp b/tools/test-environment.lisp
index d619d5c461a511f4db966fd9143f15d81d2bf319..8e58fd6c7f65890b0d8ac0bf7447fe11f14b6866 100644
--- a/tools/test-environment.lisp
+++ b/tools/test-environment.lisp
@@ -220,7 +220,7 @@ and which systems to test loading with ASDF_TEST_SYSTEMS or s=
 (defun run-test-lisp (activity forms &key (output t) log lisp debugger)
   ;; Activity is of the form "compiling ASDF", "running this test", etc.
   (format t "~&Now ~A...~@[ (log in ~A)~]~%" activity log)
-  (let* ((eval (compose-non-special-string forms))
+  (let* ((eval (compose-non-special-string forms)) ;; at least avoiding ~% is necessary on Windows.
          (command (lisp-invocation-arglist :implementation-type (get-lisp lisp)
                                            :eval eval :debugger debugger))
          (interactive (if (eq output :interactive) :interactive nil))