diff --git a/tools/testing/selftests/kselftest/ktap_helpers.sh b/tools/testing/selftests/kselftest/ktap_helpers.sh
index 79a125eb24c2e..14e7f3ec3f84c 100644
--- a/tools/testing/selftests/kselftest/ktap_helpers.sh
+++ b/tools/testing/selftests/kselftest/ktap_helpers.sh
@@ -40,7 +40,7 @@ ktap_skip_all() {
 __ktap_test() {
 	result="$1"
 	description="$2"
-	directive="$3" # optional
+	directive="${3:-}" # optional
 
 	local directive_str=
 	[ ! -z "$directive" ] && directive_str="# $directive"