diff --git a/attachment_s3/models/ir_attachment.py b/attachment_s3/models/ir_attachment.py
index e573b98..5fb3f3c 100644
--- a/attachment_s3/models/ir_attachment.py
+++ b/attachment_s3/models/ir_attachment.py
@@ -9,6 +9,7 @@ import io
 from urllib.parse import urlsplit
 
 from odoo import _, api, exceptions, models
+from odoo.addons.base.models.ir_attachment import IrAttachment as BaseIrAttachment
 from ..s3uri import S3Uri
 
 _logger = logging.getLogger(__name__)
@@ -178,9 +179,38 @@ class IrAttachment(models.Model):
         else:
             return super(IrAttachment, self)._store_file_read(fname, bin_size)
 
+    def _inverse_datas(self):
+        location = self._storage()
+        for attach in self:
+            # compute the fields that depend on datas
+            value = attach.datas
+            bin_data = base64.b64decode(value) if value else b''
+            vals = {
+                'file_size': len(bin_data),
+                'checksum': self._compute_checksum(bin_data),
+                'index_content': self._index(
+                    bin_data, attach.datas_fname,
+                    attach.mimetype),
+                'store_fname': False,
+                'db_datas': value,
+            }
+            if value and location != 'db':
+                # save it to the filestore
+                self = self.with_context(mimetype=attach.mimetype)
+                vals['store_fname'] = self._file_write(value, vals['checksum'])
+                vals['db_datas'] = False
+
+            # take current location in filestore to possibly garbage-collect it
+            fname = attach.store_fname
+            # write as superuser, as user probably does not have write access
+            super(BaseIrAttachment, attach.sudo()).write(vals)
+            if fname:
+                self._file_delete(fname)
+
     @api.model
     def _store_file_write(self, key, bin_data):
         location = self.env.context.get('storage_location') or self._storage()
+        mimetype = self.env.context.get('mimetype')
         if location == 's3':
             bucket = self._get_s3_bucket()
             obj = bucket.Object(key=key)
@@ -189,7 +219,10 @@ class IrAttachment(models.Model):
                 file.seek(0)
                 filename = 's3://%s/%s' % (bucket.name, key)
                 try:
-                    obj.upload_fileobj(file)
+                    if mimetype:
+                        obj.upload_fileobj(file, ExtraArgs={'ContentType': mimetype})
+                    else:
+                        obj.upload_fileobj(file)
                 except ClientError as error:
                     # log verbose error from s3, return short message for user
                     _logger.exception(