diff --git a/materialize-boilerplate/validate.go b/materialize-boilerplate/validate.go
index ddd48577a9..aac5cc1a55 100644
--- a/materialize-boilerplate/validate.go
+++ b/materialize-boilerplate/validate.go
@@ -89,7 +89,7 @@ func (v Validator) ValidateBinding(
 		hasDefault := p.Inference.DefaultJson != nil
 
 		if !mustExist && !hasDefault {
-			return nil, fmt.Errorf("cannot materialize collection with nullable key field '%s' unless it has a default value annotation", p.Field)
+			return nil, fmt.Errorf("materialized collection key field '%s' must be required and non-nullable, or have a default value annotation", p.Field)
 		}
 	}