diff --git a/kiss b/kiss
index c315a47..18e087f 100755
--- a/kiss
+++ b/kiss
@@ -1657,13 +1657,14 @@ main() {
 
     # Create the required temporary directories and set the variables which
     # point to them.
-    mkdir -p "${cac_dir:=${XDG_CACHE_HOME:-$HOME/.cache}/kiss}" \
-             "${mak_dir:=${KISS_TMPDIR:=$cac_dir}/build-$pid}" \
-             "${pkg_dir:=${KISS_TMPDIR:=$cac_dir}/pkg-$pid}" \
-             "${tar_dir:=${KISS_TMPDIR:=$cac_dir}/extract-$pid}" \
-             "${src_dir:=$cac_dir/sources}" \
-             "${log_dir:=$cac_dir/logs}" \
-             "${bin_dir:=$cac_dir/bin}"
+    mkdir -p \
+        "${cac_dir:=${XDG_CACHE_HOME:-${HOME:?HOME is NULL}/.cache}/kiss}" \
+         "${mak_dir:=${KISS_TMPDIR:=$cac_dir}/build-$pid}" \
+         "${pkg_dir:=${KISS_TMPDIR:=$cac_dir}/pkg-$pid}" \
+         "${tar_dir:=${KISS_TMPDIR:=$cac_dir}/extract-$pid}" \
+         "${src_dir:=$cac_dir/sources}" \
+         "${log_dir:=$cac_dir/logs}" \
+         "${bin_dir:=$cac_dir/bin}"
 
     args "$@"
 }