diff --git a/src/rer/newsletter/browser/message/messagepreview.py b/src/rer/newsletter/browser/message/messagepreview.py
index 3a9a2d8f..59da806a 100644
--- a/src/rer/newsletter/browser/message/messagepreview.py
+++ b/src/rer/newsletter/browser/message/messagepreview.py
@@ -31,7 +31,8 @@ def getMessageStyle(self):
                 break
         if not channel:
             return DEFAULT_STYLES
-        return DEFAULT_STYLES + getattr(channel, "css_style", "")
+        channel_styles = getattr(channel, "css_style", "") or ""
+        return DEFAULT_STYLES + channel_styles
 
     @property
     def channel(self):