diff --git a/action.sh b/action.sh
index fbcf928..a69f35b 100755
--- a/action.sh
+++ b/action.sh
@@ -21,7 +21,7 @@ if [ ! -d "${INPUT_DIRECTORY}" ]; then
 fi
 
 # optionally: create index
-if [ "${INPUT_INDEX}" ]; then
+if "${INPUT_INDEX}"; then
   if [ ! -e "${INPUT_DIRECTORY}/index.html" ]; then
   tree "${INPUT_DIRECTORY}" -a -H "." \
     -D \