diff --git a/agetar b/agetar
index 49a9b9c..6e5cdc0 100755
--- a/agetar
+++ b/agetar
@@ -6,7 +6,7 @@ set -euf
 BN="${0##*/}"
 export POSIXLY_CORRECT=1
 
-if [ "${NO_COLOR:-}" ]; then
+if [ -n "${NO_COLOR:-}" ]; then
 	RED="" RESET=""
 fi
 
@@ -58,7 +58,7 @@ while getopts :hedo:apr:R:i: OPT; do
 		h) usage && exit 0 ;;
 		e) TYPE=e; AGEOPTS="$AGEOPTS -e" ;;
 		d) TYPE=d; AGEOPTS="$AGEOPTS -d" ;;
-		o) [ ! "${OUTPUT:-}" ] && OUTPUT="$OPTARG" || fail "don't specify output twice D:" ;;
+		o) [ -z "${OUTPUT:-}" ] && OUTPUT="$OPTARG" || fail "don't specify output twice D:" ;;
 		a) AGEOPTS="$AGEOPTS -a" ;;
 		p) AGEOPTS="$AGEOPTS -p" ;;
 		r) RECIPIENTS="$RECIPIENTS -r '$(printf '%s' "$OPTARG" | sed -e "s/'/'\\\\''/g")'" ;;
@@ -70,7 +70,7 @@ done
 shift $((OPTIND - 1))
 
 [ "$#" -lt 1 ] && usage && exit 1
-[ ! "${TYPE:-}" ] && fail 'specify one of -e or -d'
+[ -z "${TYPE:-}" ] && fail 'specify one of -e or -d'
 
 TAR="$(mktemp)"
 trap 'rm "$TAR"' INT HUP QUIT EXIT