diff --git a/gtk/gtkcsstypesprivate.h b/gtk/gtkcsstypesprivate.h
index a1fe7105d3..28ecc7d168 100644
--- a/gtk/gtkcsstypesprivate.h
+++ b/gtk/gtkcsstypesprivate.h
@@ -93,6 +93,7 @@ typedef struct _GtkCssStaticStyle GtkCssStaticStyle;
 #define GTK_CSS_CHANGE_TIMESTAMP                      (1ULL << 50)
 #define GTK_CSS_CHANGE_ANIMATIONS                     (1ULL << 51)
 
+#define GTK_CSS_CHANGE_RESERVED_BIT                   (1ULL << 62)
 
 typedef guint64 GtkCssChange;