diff --git a/dom/interfaces.html b/dom/interfaces.html
index 8d2134f7421f4..67123d26651d3 100644
--- a/dom/interfaces.html
+++ b/dom/interfaces.html
@@ -334,7 +334,7 @@
   void setStartAfter(Node refNode);
   void setEndBefore(Node refNode);
   void setEndAfter(Node refNode);
-  void collapse(boolean toStart);
+  void collapse(optional boolean toStart = false);
   void selectNode(Node refNode);
   void selectNodeContents(Node refNode);