diff --git a/gtk/gtkscrolledwindow.c b/gtk/gtkscrolledwindow.c
index 3a965ac8f2..5e3f9ea949 100644
--- a/gtk/gtkscrolledwindow.c
+++ b/gtk/gtkscrolledwindow.c
@@ -128,6 +128,8 @@
  * # CSS nodes
  *
  * GtkScrolledWindow has a main CSS node with name scrolledwindow.
+ * It gets a .frame style class added when #GtkScrolledWindow:has-frame
+ * is %TRUE.
  *
  * It uses subnodes with names overshoot and undershoot to
  * draw the overflow and underflow indications. These nodes get