diff --git a/product/ERP5Type/Constraint/CategoryAcquiredMembershipArity.py b/product/ERP5Type/Constraint/CategoryAcquiredMembershipArity.py
index 8142f4b884f7926c3973873f0d430871de80a83a..4e96b95aedb52b88d95de903d0e181dfe336c9a7 100644
--- a/product/ERP5Type/Constraint/CategoryAcquiredMembershipArity.py
+++ b/product/ERP5Type/Constraint/CategoryAcquiredMembershipArity.py
@@ -67,7 +67,7 @@ class CategoryAcquiredMembershipArity(Constraint):
                                                  portal_type=portal_type))
     if (arity < min_arity) or (arity > max_arity):
       # Generate error message
-      error_message = "Arrity error for relation '%s'" % \
+      error_message = "Arity error for relation '%s'" % \
                       base_category
       if portal_type is not ():
         error_message += " and portal_type: '%s'" % str(portal_type)