diff --git a/mdb/collection.go b/mdb/collection.go
index 3a15fb1..57970a8 100644
--- a/mdb/collection.go
+++ b/mdb/collection.go
@@ -237,6 +237,27 @@ func (c *Collection[T]) update(tx *Snapshot, userItem *T) error {
 	return nil
 }
 
+func (c *Collection[T]) UpdateFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	if tx == nil {
+		return c.db.Update(func(tx *Snapshot) error {
+			return c.updateFunc(tx, id, update)
+		})
+	}
+	return c.updateFunc(tx, id, update)
+}
+
+func (c *Collection[T]) updateFunc(tx *Snapshot, id uint64, update func(item *T) error) error {
+	item := c.Get(tx, id)
+	if item == nil {
+		return errs.NotFound
+	}
+	if err := update(item); err != nil {
+		return err
+	}
+	c.setID(item, id) // Don't allow the ID to change.
+	return c.update(tx, item)
+}
+
 func (c *Collection[T]) Upsert(tx *Snapshot, item *T) error {
 	if tx == nil {
 		return c.db.Update(func(tx *Snapshot) error {