diff --git a/utils/reflect.go b/utils/reflect.go
index 9b8c5d1ab..935bd5dc1 100644
--- a/utils/reflect.go
+++ b/utils/reflect.go
@@ -325,7 +325,7 @@ func GreaterThan(item, oItem interface{}, orEqual bool) (gte bool, err error) {
 func Sum(items ...interface{}) (sum interface{}, err error) {
 	//we need at least 2 items to sum them
 	if len(items) < 2 {
-		return nil, fmt.Errorf("Not enough parameters : %s", len(items))
+		return nil, fmt.Errorf("Not enough parameters : %d", len(items))
 	}
 
 	// convert the type for first item