diff --git a/src/nullptr.h b/src/nullptr.h
index 84979c79..40cdcd50 100644
--- a/src/nullptr.h
+++ b/src/nullptr.h
@@ -110,7 +110,7 @@ private:
 const nullptr_t nullptr = {};
 
 #else
-    #include <cstddef>
+    #include <stddef.h>
 #endif
 #endif