diff --git a/product/CMFActivity/ActivityTool.py b/product/CMFActivity/ActivityTool.py
index 7674cb84d30f14146761a533e060b78c5415c967..b44762c82edf4102af16cc4fa7363eb3a156290f 100644
--- a/product/CMFActivity/ActivityTool.py
+++ b/product/CMFActivity/ActivityTool.py
@@ -252,7 +252,7 @@ class Message:
       newSecurityManager(None, user)
     else :
       LOG("CMFActivity", WARNING,
-          "Unable to find user %s in the portal" % user_name)
+          "Unable to find user %r in the portal" % user_name)
       noSecurityManager()
     return user