diff --git a/t/README b/t/README
index 78c9e6575c8a1f1060aada39dc5043eea807ac1c..165e7cf34da32663a18f4c6a87dbe3087dac8263 100644
--- a/t/README
+++ b/t/README
@@ -79,6 +79,10 @@ appropriately before running "make".
 --debug::
 	This may help the person who is developing a new test.
 	It causes the command defined with test_debug to run.
+	The "trash" directory (used to store all temporary data
+	during testing) is not deleted even if there are no
+	failed tests so that you can inspect its contents after
+	the test finished.
 
 --immediate::
 	This causes the test to immediately exit upon the first