diff --git a/product/ERP5/mixin/downloadable.py b/product/ERP5/mixin/downloadable.py
index 2fbfbb0e30fc3f627ccb886401109daba611926b..fbcb5defbed12bc1f30a041942a1a631520b158a 100644
--- a/product/ERP5/mixin/downloadable.py
+++ b/product/ERP5/mixin/downloadable.py
@@ -80,7 +80,7 @@ class DownloadableMixin:
       format = None
     self._checkConversionFormatPermission(format, **kw)
     mime, data = self.convert(format, **kw)
-    if not format:
+    if not format and mime != "":
       # Guess the format from original mimetype
       mimetypes_registry = getToolByName(self.getPortalObject(),
                                                           'mimetypes_registry')