diff --git a/docs/reference/gtk/gtk3-sections.txt b/docs/reference/gtk/gtk3-sections.txt
index a792e4121d..e37a61fb63 100644
--- a/docs/reference/gtk/gtk3-sections.txt
+++ b/docs/reference/gtk/gtk3-sections.txt
@@ -5966,6 +5966,7 @@ GTK_STYLE_CLASS_CALENDAR
 GTK_STYLE_CLASS_CELL
 GTK_STYLE_CLASS_COMBOBOX_ENTRY
 GTK_STYLE_CLASS_CHECK
+GTK_STYLE_CLASS_CSD
 GTK_STYLE_CLASS_CURSOR_HANDLE
 GTK_STYLE_CLASS_DEFAULT
 GTK_STYLE_CLASS_DESTRUCTIVE_ACTION
diff --git a/gtk/gtkstylecontext.h b/gtk/gtkstylecontext.h
index 1bab4394d6..8a8351c455 100644
--- a/gtk/gtkstylecontext.h
+++ b/gtk/gtkstylecontext.h
@@ -248,6 +248,16 @@ struct _GtkStyleContextClass
  */
 #define GTK_STYLE_CLASS_RUBBERBAND "rubberband"
 
+/**
+ * GTK_STYLE_CLASS_CSD:
+ *
+ * A CSS class that gets added to windows which have
+ * client-side decorations.
+ *
+ * Since: 3.14
+ */
+#define GTK_STYLE_CLASS_CSD "csd"
+
 /**
  * GTK_STYLE_CLASS_TOOLTIP:
  *