diff --git a/NEWS b/NEWS
index a9124af1..cd86dc60 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,10 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
     . Internal change
 ==========================
 
+4.8.0, unknown release date
+- alt truncation could result in malformed UTF-8 sequence. Don't
+  truncate.  Thanks Brandon Farber for reporting.
+
 4.7.0, released 2015-08-04
 # opacity is now considered a "tricky" CSS property rather than a
   proprietary one.
diff --git a/library/HTMLPurifier/AttrTransform/ImgRequired.php b/library/HTMLPurifier/AttrTransform/ImgRequired.php
index 7df6cb3e..235ebb34 100644
--- a/library/HTMLPurifier/AttrTransform/ImgRequired.php
+++ b/library/HTMLPurifier/AttrTransform/ImgRequired.php
@@ -32,8 +32,7 @@ class HTMLPurifier_AttrTransform_ImgRequired extends HTMLPurifier_AttrTransform
             if ($src) {
                 $alt = $config->get('Attr.DefaultImageAlt');
                 if ($alt === null) {
-                    // truncate if the alt is too long
-                    $attr['alt'] = substr(basename($attr['src']), 0, 40);
+                    $attr['alt'] = basename($attr['src']);
                 } else {
                     $attr['alt'] = $alt;
                 }