diff --git a/initrd/install.h b/initrd/install.h
index 4d4aaf4..019864c 100644
--- a/initrd/install.h
+++ b/initrd/install.h
@@ -6,8 +6,8 @@
 		PREREQ
 
 		# tcsd exits if it doesn't have tss group and user
-		grep tss /etc/group  >> "${TARGET_DIR:-MUST_EXIST}/etc/group"
-		grep tss /etc/passwd >> "${TARGET_DIR:-MUST_EXIST}/etc/passwd"
+		grep tss /etc/group  >> "${TARGET_DIR:?must exist}/etc/group"
+		grep tss /etc/passwd >> "${TARGET_DIR:?must exist}/etc/passwd"
 
 		for f in /lib/udev/rules.d/*tpm*; do
 			INST_UDEV "$f"
@@ -15,13 +15,13 @@
 
 		if [ -e /etc/tcsd.conf ]; then
 			INST_CFG /etc/tcsd.conf
-			chown root:tss "${TARGET_DIR:-MUST_EXIST}/etc/tcsd.conf"
+			chown root:tss "${TARGET_DIR:?must exist}/etc/tcsd.conf"
 			system_ps_file="$(awk -F '[[:space:]]*=[[:space:]]*' '!/^[[:space:]]*#/ && !/^$/ && $1 ~ /system_ps_file$/ {gsub(/[[:space:]]*$/, "", $2); print $2}' /etc/tcsd.conf)"
 			system_ps_file="${system_ps_file:-/var/lib/tpm/system.data}"
 		fi
 
 		# tcsd can't find SRK if state not present, refuses to start if it doesn't have parent to tss dir
-		mkdir -p "${TARGET_DIR:-MUST_EXIST}/$(dirname "$(dirname "$system_ps_file")")"
+		mkdir -p "${TARGET_DIR:?must exist}/$(dirname "$(dirname "$system_ps_file")")"
 		[ -f "$system_ps_file" ] && INST_STATE "$system_ps_file"
 	}