diff --git a/tools/binman/README b/tools/binman/README
index 7eda244..2f4c7fe 100644
--- a/tools/binman/README
+++ b/tools/binman/README
@@ -731,6 +731,14 @@
 being used (-T) since they are incompatible.
 
 
+Debugging tests
+---------------
+
+Sometimes when debugging tests it is useful to keep the input and output
+directories so they can be examined later. Use -X or --test-preserve-dirs for
+this.
+
+
 Advanced Features / Technical docs
 ----------------------------------