diff --git a/phpseclib/File/ASN1.php b/phpseclib/File/ASN1.php
index a9f20e05..802661e2 100644
--- a/phpseclib/File/ASN1.php
+++ b/phpseclib/File/ASN1.php
@@ -316,6 +316,9 @@ class File_ASN1
     {
         $current = array('start' => $start);
 
+        if (!isset($encoded[$encoded_pos])) {
+            return false;
+        }
         $type = ord($encoded[$encoded_pos++]);
         $startOffset = 1;
 
@@ -326,6 +329,9 @@ class File_ASN1
             $tag = 0;
             // process septets (since the eighth bit is ignored, it's not an octet)
             do {
+                if (!isset($encoded[$encoded_pos])) {
+                    return false;
+                }
                 $temp = ord($encoded[$encoded_pos++]);
                 $startOffset++;
                 $loop = $temp >> 7;
@@ -342,6 +348,9 @@ class File_ASN1
         $start+= $startOffset;
 
         // Length, as discussed in paragraph 8.1.3 of X.690-0207.pdf#page=13
+        if (!isset($encoded[$encoded_pos])) {
+            return false;
+        }
         $length = ord($encoded[$encoded_pos++]);
         $start++;
         if ($length == 0x80) { // indefinite length
diff --git a/phpseclib/File/X509.php b/phpseclib/File/X509.php
index 428e677f..cf342472 100644
--- a/phpseclib/File/X509.php
+++ b/phpseclib/File/X509.php
@@ -1652,7 +1652,6 @@ class File_X509
                 $id = $extensions[$i]['extnId'];
                 $value = &$extensions[$i]['extnValue'];
                 $value = base64_decode($value);
-                $decoded = $asn1->decodeBER($value);
                 /* [extnValue] contains the DER encoding of an ASN.1 value
                    corresponding to the extension type identified by extnID */
                 $map = $this->_getMapping($id);
@@ -1660,6 +1659,7 @@ class File_X509
                     $decoder = $id == 'id-ce-nameConstraints' ?
                         array($this, '_decodeNameConstraintIP') :
                         array($this, '_decodeIP');
+                    $decoded = $asn1->decodeBER($value);
                     $mapped = $asn1->asn1map($decoded[0], $map, array('iPAddress' => $decoder));
                     $value = $mapped === false ? $decoded[0] : $mapped;
 
diff --git a/tests/Unit/File/X509/X509Test.php b/tests/Unit/File/X509/X509Test.php
index 2702feb6..9e133dc6 100644
--- a/tests/Unit/File/X509/X509Test.php
+++ b/tests/Unit/File/X509/X509Test.php
@@ -862,4 +862,38 @@ qzFkAKWjJj4KjfrbZX4C0Spfxw==
 
         $this->assertIsArray($r);
     }
+
+    /**
+     * @group github1676
+     */
+    public function testMalformedExt()
+    {
+        $a = '-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----';
+
+        $x509 = new File_X509();
+        $r = $x509->loadX509($a);
+
+        $this->assertIsArray($r);
+    }
 }