diff --git a/phpseclib/File/ASN1.php b/phpseclib/File/ASN1.php
index b225e953..c4b983b5 100644
--- a/phpseclib/File/ASN1.php
+++ b/phpseclib/File/ASN1.php
@@ -440,6 +440,9 @@ abstract class ASN1
                 break;
             case self::TYPE_OBJECT_IDENTIFIER:
                 $current['content'] = self::decodeOID(substr($content, $content_pos));
+                if ($current['content'] === false) {
+                    return false;
+                }
                 break;
             /* Each character string type shall be encoded as if it had been declared:
                [UNIVERSAL x] IMPLICIT OCTET STRING
@@ -1143,6 +1146,11 @@ abstract class ASN1
         $oid = [];
         $pos = 0;
         $len = strlen($content);
+
+        if (ord($content[$len - 1]) & 0x80) {
+            return false;
+        }
+
         $n = new BigInteger();
         while ($pos < $len) {
             $temp = ord($content[$pos++]);