diff --git a/libc/src/__support/CPP/type_traits/remove_all_extents.h b/libc/src/__support/CPP/type_traits/remove_all_extents.h
index 7799032ad52556..54b36a4c2e5463 100644
--- a/libc/src/__support/CPP/type_traits/remove_all_extents.h
+++ b/libc/src/__support/CPP/type_traits/remove_all_extents.h
@@ -11,6 +11,8 @@
 #include "src/__support/CPP/type_traits/type_identity.h"
 #include "src/__support/macros/config.h"
 
+#include <stddef.h> // size_t
+
 namespace __llvm_libc::cpp {
 
 // remove_all_extents