diff --git a/boards/forms.py b/boards/forms.py
--- a/boards/forms.py
+++ b/boards/forms.py
@@ -55,6 +55,7 @@ MIMETYPE_EXTENSIONS = {
     'application/pdf': 'pdf',
     'x-diff': 'diff',
     'image/svg+xml': 'svg',
+    'application/x-shockwave-flash': 'swf',
 }
 
 
diff --git a/boards/models/attachment/__init__.py b/boards/models/attachment/__init__.py
--- a/boards/models/attachment/__init__.py
+++ b/boards/models/attachment/__init__.py
@@ -2,7 +2,7 @@ from django.db import models
 
 from boards import utils
 from boards.models.attachment.viewers import get_viewers, AbstractViewer
-from boards.utils import get_upload_filename, get_file_mimetype
+from boards.utils import get_upload_filename, get_file_mimetype, get_extension
 
 
 class AttachmentManager(models.Manager):
@@ -13,7 +13,7 @@ class AttachmentManager(models.Manager):
             attachment = existing[0]
         else:
             # FIXME Use full mimetype here, need to modify viewers too
-            file_type = get_file_mimetype(file).split('/')[-1]
+            file_type = get_extension(file.name)
             attachment = self.create(file=file, mimetype=file_type,
                                      hash=file_hash)
 
diff --git a/boards/utils.py b/boards/utils.py
--- a/boards/utils.py
+++ b/boards/utils.py
@@ -127,9 +127,13 @@ def validate_file_size(size: int):
             % str(max_size))
 
 
+def get_extension(filename):
+    return filename.split(FILE_EXTENSION_DELIMITER)[-1:][0]
+
+
 def get_upload_filename(model_instance, old_filename):
     # TODO Use something other than random number in file name
-    extension = old_filename.split(FILE_EXTENSION_DELIMITER)[-1:][0]
+    extension = get_extension(old_filename)
     new_name = '{}{}.{}'.format(
         str(int(time.mktime(time.gmtime()))),
         str(int(random() * 1000)),