diff --git a/gtk/gtkexpander.c b/gtk/gtkexpander.c
index 8fc88d40c1..6e9b4305a8 100644
--- a/gtk/gtkexpander.c
+++ b/gtk/gtkexpander.c
@@ -957,7 +957,7 @@ gtk_expander_measure (GtkWidget      *widget,
 
 /**
  * gtk_expander_new:
- * @label: the text of the label
+ * @label: (nullable): the text of the label
  *
  * Creates a new expander using @label as the text of the label.
  *