diff --git a/libcxx/include/chrono b/libcxx/include/chrono
--- a/libcxx/include/chrono
+++ b/libcxx/include/chrono
@@ -681,6 +681,7 @@
 #include <__chrono/year_month_day.h>
 #include <__chrono/year_month_weekday.h>
 #include <__config>
+#include <format>
 #include <version>
 
 // standard-mandated includes