diff -u b/core/lib/Drupal/Core/File/MimeType/ExtensionMimeTypeGuesser.php b/core/lib/Drupal/Core/File/MimeType/ExtensionMimeTypeGuesser.php
--- b/core/lib/Drupal/Core/File/MimeType/ExtensionMimeTypeGuesser.php
+++ b/core/lib/Drupal/Core/File/MimeType/ExtensionMimeTypeGuesser.php
@@ -227,8 +227,9 @@
       198 => 'audio/x-scpls',
       199 => 'audio/x-sd2',
       200 => 'audio/x-wav',
-      360 => 'audio/aac' ,
-      112 => 'audio/flac' ,
+      360 => 'audio/aac',
+      112 => 'audio/flac',
+      201 => 'chemical/x-alchemy',
       201 => 'chemical/x-alchemy',
       202 => 'chemical/x-cache',
       203 => 'chemical/x-cache-csf',