diff --git a/src/ORM/FieldType/DBText.php b/src/ORM/FieldType/DBText.php
index c719a525d4d..e64d4c421dd 100644
--- a/src/ORM/FieldType/DBText.php
+++ b/src/ORM/FieldType/DBText.php
@@ -206,8 +206,8 @@ public function ContextSummary(
         if ($position > 0) {
             // We don't want to start mid-word
             $position = max(
-                (int) mb_strrpos(substr($text, 0, $position), ' '),
-                (int) mb_strrpos(substr($text, 0, $position), "\n")
+                (int) mb_strrpos(mb_substr($text, 0, $position), ' '),
+                (int) mb_strrpos(mb_substr($text, 0, $position), "\n")
             );
         }