diff --git a/src/utils/utf8.php b/src/utils/utf8.php
--- a/src/utils/utf8.php
+++ b/src/utils/utf8.php
@@ -718,7 +718,12 @@
         'mbstring'));
   }
 
-  $result = @mb_convert_encoding($string, $to_encoding, $from_encoding);
+  $available_encodings = mb_list_encodings();
+  if (in_array($to_encoding, $available_encodings, true)) {
+    $result = @mb_convert_encoding($string, $to_encoding, $from_encoding);
+  } else {
+    $result = false;
+  }
 
   if ($result === false) {
     $message = error_get_last();