diff --git a/tests/run-make/libtest-junit/validate_junit.py b/tests/run-make/libtest-junit/validate_junit.py
index 0d9b34a3cf7..f92473751b0 100755
--- a/tests/run-make/libtest-junit/validate_junit.py
+++ b/tests/run-make/libtest-junit/validate_junit.py
@@ -1,5 +1,15 @@
 #!/usr/bin/env python
 
+# Trivial Python script that reads lines from stdin, and checks that each line
+# is a well-formed XML document.
+#
+# This takes advantage of the fact that Python has a built-in XML parser,
+# whereas doing the same check in Rust would require us to pull in an XML
+# crate just for this relatively-minor test.
+#
+# If you're trying to remove Python scripts from the test suite, think twice
+# before removing this one. You could do so, but it's probably not worth it.
+
 import sys
 import xml.etree.ElementTree as ET