diff -u b/core/modules/file/src/Plugin/migrate/process/UrlEncode.php b/core/modules/file/src/Plugin/migrate/process/UrlEncode.php
--- b/core/modules/file/src/Plugin/migrate/process/UrlEncode.php
+++ b/core/modules/file/src/Plugin/migrate/process/UrlEncode.php
@@ -27,7 +27,7 @@
         $components[$key] = rawurlencode($component);
       }
       $value = implode('/', $components);
-      // Actually, we don't want certain characters encoded.
+      // Do not encode URL syntax characters.
       $value = str_replace(['%3A', '%3F', '%26'], [':', '?', '&'], $value);
     }
     return $value;