diff --git a/src/Illuminate/Encryption/Encrypter.php b/src/Illuminate/Encryption/Encrypter.php
index f369cfbd4d08..a4351c99285d 100755
--- a/src/Illuminate/Encryption/Encrypter.php
+++ b/src/Illuminate/Encryption/Encrypter.php
@@ -83,7 +83,7 @@ public static function supported($key, $cipher)
      */
     public static function generateKey($cipher)
     {
-        return random_bytes(self::$supportedCiphers[$cipher]['size']);
+        return random_bytes(self::$supportedCiphers[$cipher]['size'] ?? 32);
     }
 
     /**