diff --git a/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php b/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php
index e5fb276e..96a434c0 100644
--- a/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php
+++ b/phpseclib/Crypt/Common/Formats/Keys/OpenSSH.php
@@ -202,7 +202,7 @@ abstract class OpenSSH
      */
     protected static function wrapPrivateKey($publicKey, $privateKey, $password, $options)
     {
-        if (!empty($password) || is_string($password)) {
+        if (!empty($password) && is_string($password)) {
             throw new UnsupportedFormatException('Encrypted OpenSSH private keys are not supported');
         }
 
diff --git a/phpseclib/Crypt/EC/Formats/Keys/MontgomeryPrivate.php b/phpseclib/Crypt/EC/Formats/Keys/MontgomeryPrivate.php
index b908adc1..3cd22d42 100644
--- a/phpseclib/Crypt/EC/Formats/Keys/MontgomeryPrivate.php
+++ b/phpseclib/Crypt/EC/Formats/Keys/MontgomeryPrivate.php
@@ -27,6 +27,7 @@ use phpseclib3\Crypt\EC\Curves\Curve448;
 use phpseclib3\Crypt\EC\BaseCurves\Montgomery as MontgomeryCurve;
 use phpseclib3\Math\Common\FiniteField\Integer;
 use phpseclib3\Math\BigInteger;
+use phpseclib3\Exception\UnsupportedFormatException;
 
 /**
  * Montgomery Curve Private Key Handler
@@ -98,6 +99,10 @@ abstract class MontgomeryPrivate
      */
     public static function savePrivateKey(Integer $privateKey, MontgomeryCurve $curve, array $publicKey, $password = '')
     {
+        if (!empty($password) && is_string($password)) {
+            throw new UnsupportedFormatException('MontgomeryPrivate private keys do not support encryption');
+        }
+
         return $privateKey->toBytes();
     }
 }
diff --git a/phpseclib/Crypt/EC/Formats/Keys/libsodium.php b/phpseclib/Crypt/EC/Formats/Keys/libsodium.php
index 8b7f6f7d..b8be1944 100644
--- a/phpseclib/Crypt/EC/Formats/Keys/libsodium.php
+++ b/phpseclib/Crypt/EC/Formats/Keys/libsodium.php
@@ -21,6 +21,7 @@ namespace phpseclib3\Crypt\EC\Formats\Keys;
 
 use phpseclib3\Crypt\EC\Curves\Ed25519;
 use phpseclib3\Math\Common\FiniteField\Integer;
+use phpseclib3\Exception\UnsupportedFormatException;
 
 /**
  * libsodium Key Handler
@@ -113,6 +114,9 @@ abstract class libsodium
         if (strlen($privateKey->secret) != 32) {
             throw new \RuntimeException('Private Key secret is not of the correct length');
         }
+        if (!empty($password) && is_string($password)) {
+            throw new UnsupportedFormatException('libsodium private keys do not support encryption');
+        }
         return $privateKey->secret . $curve->encodePoint($publicKey);
     }
 }
diff --git a/phpseclib/Crypt/RSA/Formats/Keys/MSBLOB.php b/phpseclib/Crypt/RSA/Formats/Keys/MSBLOB.php
index 60dff682..06469913 100644
--- a/phpseclib/Crypt/RSA/Formats/Keys/MSBLOB.php
+++ b/phpseclib/Crypt/RSA/Formats/Keys/MSBLOB.php
@@ -22,6 +22,7 @@ namespace phpseclib3\Crypt\RSA\Formats\Keys;
 use ParagonIE\ConstantTime\Base64;
 use phpseclib3\Math\BigInteger;
 use phpseclib3\Common\Functions\Strings;
+use phpseclib3\Exception\UnsupportedFormatException;
 
 /**
  * Microsoft BLOB Formatted RSA Key Handler
@@ -191,6 +192,10 @@ abstract class MSBLOB
             throw new \InvalidArgumentException('MSBLOB does not support multi-prime RSA keys');
         }
 
+        if (!empty($password) && is_string($password)) {
+            throw new UnsupportedFormatException('MSBLOB private keys do not support encryption');
+        }
+
         $n = strrev($n->toBytes());
         $e = str_pad(strrev($e->toBytes()), 4, "\0");
         $key = pack('aavV', chr(self::PRIVATEKEYBLOB), chr(2), 0, self::CALG_RSA_KEYX);
diff --git a/phpseclib/Crypt/RSA/Formats/Keys/XML.php b/phpseclib/Crypt/RSA/Formats/Keys/XML.php
index 9d3d2822..ef51c783 100644
--- a/phpseclib/Crypt/RSA/Formats/Keys/XML.php
+++ b/phpseclib/Crypt/RSA/Formats/Keys/XML.php
@@ -24,6 +24,7 @@ namespace phpseclib3\Crypt\RSA\Formats\Keys;
 
 use ParagonIE\ConstantTime\Base64;
 use phpseclib3\Math\BigInteger;
+use phpseclib3\Exception\UnsupportedFormatException;
 
 /**
  * XML Formatted RSA Key Handler
@@ -136,6 +137,11 @@ abstract class XML
         if (count($primes) != 2) {
             throw new \InvalidArgumentException('XML does not support multi-prime RSA keys');
         }
+
+        if (!empty($password) && is_string($password)) {
+            throw new UnsupportedFormatException('XML private keys do not support encryption');
+        }
+
         return "<RSAKeyPair>\r\n" .
                '  <Modulus>' . Base64::encode($n->toBytes()) . "</Modulus>\r\n" .
                '  <Exponent>' . Base64::encode($e->toBytes()) . "</Exponent>\r\n" .