diff --git a/script/build_all.sh b/script/build_all.sh
index 3be16a5..7eecde9 100755
--- a/script/build_all.sh
+++ b/script/build_all.sh
@@ -99,7 +99,7 @@ else
     MAKEDEB_PATH="$(realpath "$MAKEDEB_PATH")"
 fi
 
-if [[ -n ${PACKAGE_DIR-} && "${#PACKAGE_DIR}" -gt 0 ]] ; then
+if [[ -n "${PACKAGE_DIR-}" && "${#PACKAGE_DIR}" -gt 0 ]] ; then
     for p in "${PACKAGE_DIR[@]}" ; do
         for f in "$p"/* ; do
             _PACKGES_TO_BUILD+=("$f")