diff --git a/tests/data/test564 b/tests/data/test564
index 72bf12919e..4c9ecd4664 100644
--- a/tests/data/test564
+++ b/tests/data/test564
@@ -1,4 +1,6 @@
 <testcase>
+# Warning: if this test fails to start the SSH server, check that none of
+# the user's shell profiles sends output to stdout of a non-interactive shell.
 <info>
 <keywords>
 FTP