diff --git a/t/lib-credential.sh b/t/lib-credential.sh
index 937b831ea6..5ea8bc9f1d 100755
--- a/t/lib-credential.sh
+++ b/t/lib-credential.sh
@@ -1,4 +1,5 @@
-#!/bin/sh
+# Shell library for testing credential handling including helpers. See t0302
+# for an example of testing a specific helper.
 
 # Try a set of credential helpers; the expected stdin,
 # stdout and stderr should be provided on stdin,