Maybe?

binder/views.py

@@ -2699,15 +2699,14 @@ def dispatch_file_field(self, request, pk=None, file_field=None):
 			try:
 				if serve_directly:
 					resp = HttpResponse(content_type=content_type)
+					resp['X-Accel-Redirect'] = '/internal/media/' + file_field.name
 				else:
 					resp = StreamingHttpResponse(file_field.open(), content_type=content_type)
 			except FileNotFoundError:
 				logger.error('Expected file {} not found'.format(file_field.name))
 				raise BinderNotFound(file_field_name)
 
 			if 'download' in request.GET:
-				if serve_directly:
-					resp['X-Accel-Redirect'] = '/internal/media/' + file_field.name
 				filename = self.filefield_get_name(instance=obj, request=request, file_field=file_field)
 				if 'prefix' in request.GET:
 					filename = request.GET['prefix'] + ' - ' + filename