diff --git a/lib/Horde/String.php b/lib/Horde/String.php
index 9e6e16b0..7f5df398 100644
--- a/lib/Horde/String.php
+++ b/lib/Horde/String.php
@@ -870,6 +870,9 @@ public static function validUtf8($text)
                 }
 
                 do {
+                    if($i + 1 >= $len) {
+                        return false;
+                    }                    
                     $c = ord($text[++$i]);
                     if (($c < 128) || ($c > 191)) {
                         return false;