diff --git a/src/PhpSpreadsheet/Shared/StringHelper.php b/src/PhpSpreadsheet/Shared/StringHelper.php
index c4945540..2273333d 100644
--- a/src/PhpSpreadsheet/Shared/StringHelper.php
+++ b/src/PhpSpreadsheet/Shared/StringHelper.php
@@ -468,7 +468,10 @@ class StringHelper
     public static function convertEncoding($value, $to, $from)
     {
         if (self::getIsIconvEnabled()) {
-            return iconv($from, $to . '//IGNORE//TRANSLIT', $value);
+            $result = iconv($from, $to . '//IGNORE//TRANSLIT', $value);
+            if (false !== $result) {
+                return $result;
+            }
         }
 
         return mb_convert_encoding($value, $to, $from);