diff --git a/product/ERP5Type/Constraint/CategoryMembershipArity.py b/product/ERP5Type/Constraint/CategoryMembershipArity.py
index 0a95c07df0de809b3696b1cf118030137a7dd7a7..872fc0507c88fdecee1d181e04192fc928d23334 100644
--- a/product/ERP5Type/Constraint/CategoryMembershipArity.py
+++ b/product/ERP5Type/Constraint/CategoryMembershipArity.py
@@ -64,7 +64,7 @@ class CategoryMembershipArity(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)