diff --git a/gtk/gtkspinner.c b/gtk/gtkspinner.c
index 3b4fc7dc63..24a4920134 100644
--- a/gtk/gtkspinner.c
+++ b/gtk/gtkspinner.c
@@ -57,7 +57,8 @@
  *
  * # CSS nodes
  *
- * GtkSpinner has a single CSS node with the name spinner.
+ * GtkSpinner has a single CSS node with the name spinner. When the animation is
+ * active, the :checked pseudoclass is added to this node.
  */