diff --git a/document.go b/document.go
index 7824d25..dfd97fe 100644
--- a/document.go
+++ b/document.go
@@ -96,13 +96,15 @@ func (d *Document) Save() error {
 	if val.Kind() == reflect.Slice {
 		for i := 0; i < val.Len(); i++ {
 			cur := val.Index(i)
-			if err := doSave(d.model.getColl(), !d.exists, cur.Interface()); err != nil {
+			asId := cur.Interface().(HasID)
+			if err := doSave(d.model.getColl(), !d.exists && reflect.ValueOf(asId.Id()).IsZero(), cur.Interface()); err != nil {
 				return err
 			}
 		}
 		return nil
 	} else {
-		return doSave(d.model.getColl(), !d.exists, d.self)
+		asId := val.Interface().(HasID)
+		return doSave(d.model.getColl(), !d.exists && reflect.ValueOf(asId.Id()).IsZero(), d.self)
 	}
 }