diff --git a/odoo/addons/base/models/assetsbundle.py b/odoo/addons/base/models/assetsbundle.py
index 43602bad89c..1bd4bbd8251 100644
--- a/odoo/addons/base/models/assetsbundle.py
+++ b/odoo/addons/base/models/assetsbundle.py
@@ -439,7 +439,7 @@ class AssetsBundle(object):
                 assets = [asset for asset in self.stylesheets if isinstance(asset, atype)]
                 if assets:
                     source = '\n'.join([asset.get_source() for asset in assets])
-                    compiled = self.compile_css(assets[0].compile, source)
+                    compiled += self.compile_css(assets[0].compile, source)
 
             # We want to run rtlcss on normal css, so merge it in compiled
             if self.user_direction == 'rtl':