diff --git a/INSTALL/CreatePersistentImg.sh b/INSTALL/CreatePersistentImg.sh
index 21d65c47..57053933 100644
--- a/INSTALL/CreatePersistentImg.sh
+++ b/INSTALL/CreatePersistentImg.sh
@@ -108,8 +108,8 @@ freeloop=$(losetup -f)
 losetup $freeloop "$outputfile"
 
 if [ ! -z "$passphrase" ]; then
-    printf "$passphrase" | cryptsetup -q --verbose luksFormat $freeloop -
-    printf "$passphrase" | cryptsetup -q --verbose luksOpen $freeloop persist_decrypted -
+    printf -- "$passphrase" | cryptsetup -q --verbose luksFormat $freeloop -
+    printf -- "$passphrase" | cryptsetup -q --verbose luksOpen $freeloop persist_decrypted -
     _freeloop=$freeloop
     freeloop="/dev/mapper/persist_decrypted"
 fi