diff --git a/lib/common.sh b/lib/common.sh
index feb5080..e826e97 100644
--- a/lib/common.sh
+++ b/lib/common.sh
@@ -58,14 +58,14 @@ stat_done() {
 }
 
 setup_workdir() {
-	[ -z "$WORKDIR" ] && WORKDIR=$(mktemp -d /tmp/$(basename $0).XXXXXXXXXX)
+	[[ -z $WORKDIR ]] && WORKDIR=$(mktemp -d /tmp/$(basename $0).XXXXXXXXXX)
 }
 
 cleanup() {
 	trap - EXIT INT QUIT TERM
 
-	[ -n "$WORKDIR" ] && rm -rf "$WORKDIR"
-	[ "$1" ] && exit $1
+	[[ -n $WORKDIR ]] && rm -rf "$WORKDIR"
+	[[ $1 ]] && exit $1
 }
 
 abort() {