diff --git a/test/test-mutual-redefinition-1.asd b/test/test-mutual-redefinition-1.asd
index 1e74af0e0589bcdf1929cf9435ff1e503db0a54a..589b64e8312720cb2c9fde2b41b1b627f054e3cb 100644
--- a/test/test-mutual-redefinition-1.asd
+++ b/test/test-mutual-redefinition-1.asd
@@ -1,2 +1,5 @@
+;; This file defines test-mutual-redefinition-1 but ALSO defines test-mutual-redefinition-2
+;; There would be an infinite loop if find-system didn't specifically avoid
+;; loading a definition twice in the same "session".
 (defsystem test-mutual-redefinition-1)
 (defsystem test-mutual-redefinition-2)
diff --git a/test/test-mutual-redefinition-2.asd b/test/test-mutual-redefinition-2.asd
index 1e74af0e0589bcdf1929cf9435ff1e503db0a54a..ff3f41c9b9a8fe303a4fcaf4a8a593fee4cbdbdd 100644
--- a/test/test-mutual-redefinition-2.asd
+++ b/test/test-mutual-redefinition-2.asd
@@ -1,2 +1,3 @@
+;; This file defines test-mutual-redefinition-2 but ALSO defines test-mutual-redefinition-1
 (defsystem test-mutual-redefinition-1)
 (defsystem test-mutual-redefinition-2)