diff --git a/kernel/setup.sh b/kernel/setup.sh
index 108d2104..856d1cd6 100755
--- a/kernel/setup.sh
+++ b/kernel/setup.sh
@@ -18,7 +18,7 @@ fi
 test -d "$GKI_ROOT/KernelSU" || git clone https://github.com/tiann/KernelSU
 cd "$GKI_ROOT/KernelSU"
 git stash && git pull
-if [ ! "$1" ]; then
+if [ -z "${1-}" ]; then
     git checkout "$(git describe --abbrev=0 --tags)"
 else
     git checkout "$1"