diff --git a/README.md b/README.md
index 83bdc0fcb..c9fe6836f 100644
--- a/README.md
+++ b/README.md
@@ -368,6 +368,8 @@ $ bash util/build-gnu.sh
 $ bash util/run-gnu-test.sh
 # To run a single test:
 $ bash util/run-gnu-test.sh tests/touch/not-owner.sh # for example
+# If this is a perl (.pl) test, to run in debug:
+$ DEBUG=1 bash util/run-gnu-test.sh tests/misc/sm3sum.pl
 ```
 
 Note that it relies on individual utilities (not the multicall binary).