diff --git a/src/cryptsetup.c b/src/cryptsetup.c
index cea4d874..60f461d0 100644
--- a/src/cryptsetup.c
+++ b/src/cryptsetup.c
@@ -1387,6 +1387,13 @@ static int action_open_luks(void)
 
 	if (opt_master_key_file) {
 		keysize = crypt_get_volume_key_size(cd);
+		if (!keysize && !opt_key_size) {
+			log_err(_("Cannot dermine volume key size for LUKS without keyslots, please use --key-size option."));
+			r = -EINVAL;
+			goto out;
+		} else if (!keysize)
+			keysize = opt_key_size / 8;
+
 		r = tools_read_mk(opt_master_key_file, &key, keysize);
 		if (r < 0)
 			goto out;
@@ -1691,6 +1698,13 @@ static int action_luksAddKey(void)
 	}
 
 	if (opt_master_key_file) {
+		if (!keysize && !opt_key_size) {
+			log_err(_("Cannot dermine volume key size for LUKS without keyslots, please use --key-size option."));
+			r = -EINVAL;
+			goto out;
+		} else if (!keysize)
+			keysize = opt_key_size / 8;
+
 		r = tools_read_mk(opt_master_key_file, &key, keysize);
 		if (r < 0)
 			goto out;
@@ -3587,9 +3601,9 @@ int main(int argc, const char **argv)
 	   strcmp(aname, "luksFormat") &&
 	   strcmp(aname, "open") &&
 	   strcmp(aname, "benchmark") &&
-	   (strcmp(aname, "luksAddKey") || !opt_unbound))
+	   strcmp(aname, "luksAddKey"))
 		usage(popt_context, EXIT_FAILURE,
-		      _("Option --key-size is allowed only for luksFormat, luksAddKey (with --unbound),\n"
+		      _("Option --key-size is allowed only for luksFormat, luksAddKey,\n"
 			"open and benchmark actions. To limit read from keyfile use --keyfile-size=(bytes)."),
 		      poptGetInvocationName(popt_context));
 
diff --git a/tests/compat-test2 b/tests/compat-test2
index 44daeaf1..04312291 100755
--- a/tests/compat-test2
+++ b/tests/compat-test2
@@ -503,7 +503,7 @@ echo $PWD1 | $CRYPTSETUP luksOpen $LOOPDEV $DEV_NAME2 2>/dev/null && fail
 $CRYPTSETUP  luksClose  $DEV_NAME || fail
 
 prepare "[21] luksDump" wipe
-echo $PWD1 | $CRYPTSETUP -q luksFormat $FAST_PBKDF_OPT --uuid $TEST_UUID --type luks2 $LOOPDEV $KEY1 || fail
+echo $PWD1 | $CRYPTSETUP -q luksFormat --key-size 256 $FAST_PBKDF_OPT --uuid $TEST_UUID --type luks2 $LOOPDEV $KEY1 || fail
 echo $PWD1 | $CRYPTSETUP luksAddKey $FAST_PBKDF_OPT $LOOPDEV -d $KEY1 || fail
 $CRYPTSETUP luksDump $LOOPDEV | grep -q "0: luks2" || fail
 $CRYPTSETUP luksDump $LOOPDEV | grep -q $TEST_UUID || fail
@@ -513,6 +513,11 @@ $CRYPTSETUP luksDump -q $LOOPDEV --dump-master-key -d $KEY1 | grep -q "MK dump:"
 echo $PWD1 | $CRYPTSETUP luksDump -q $LOOPDEV --dump-master-key --master-key-file $VK_FILE >/dev/null || fail
 echo $PWD1 | $CRYPTSETUP luksDump -q $LOOPDEV --dump-master-key --master-key-file $VK_FILE 2>/dev/null && fail
 echo $PWD1 | $CRYPTSETUP luksAddKey $FAST_PBKDF_OPT --master-key-file $VK_FILE $LOOPDEV || fail
+# Use volume key file without keyslots
+$CRYPTSETUP luksErase -q $LOOPDEV || fail
+$CRYPTSETUP luksOpen --master-key-file $VK_FILE --key-size 256 --test-passphrase $LOOPDEV || fail
+echo $PWD1 | $CRYPTSETUP luksAddKey $FAST_PBKDF_OPT --master-key-file $VK_FILE --key-size 256 $LOOPDEV || fail
+echo $PWD1 | $CRYPTSETUP luksOpen --test-passphrase $LOOPDEV || fail
 
 prepare "[22] remove disappeared device" wipe
 dmsetup create $DEV_NAME --table "0 39998 linear $LOOPDEV 2" || fail