diff --git a/libcxx/include/__format/formatter_floating_point.h b/libcxx/include/__format/formatter_floating_point.h
index 9ffe20a1a72a..a9cdfac8cb4c 100644
--- a/libcxx/include/__format/formatter_floating_point.h
+++ b/libcxx/include/__format/formatter_floating_point.h
@@ -36,6 +36,7 @@
 #include <__utility/move.h>
 #include <__utility/unreachable.h>
 #include <cmath>
+#include <cstddef/ptrdiff_t.h>
 
 #ifndef _LIBCPP_HAS_NO_LOCALIZATION
 #  include <__locale>
diff --git a/libcxx/include/__string/char_traits.h b/libcxx/include/__string/char_traits.h
index fff045be0180..f59764bb0d04 100644
--- a/libcxx/include/__string/char_traits.h
+++ b/libcxx/include/__string/char_traits.h
@@ -17,6 +17,7 @@
 #include <__assert>
 #include <__compare/ordering.h>
 #include <__config>
+#include <__cstddef/ptrdiff_t.h>
 #include <__functional/hash.h>
 #include <__functional/identity.h>
 #include <__iterator/iterator_traits.h>