diff --git a/include/mimalloc-internal.h b/include/mimalloc-internal.h
index cf4d80ea..6a449ea5 100644
--- a/include/mimalloc-internal.h
+++ b/include/mimalloc-internal.h
@@ -52,6 +52,7 @@ static inline uintptr_t _mi_random_shuffle(uintptr_t x);
 // init.c
 extern mi_decl_cache_align mi_stats_t       _mi_stats_main;
 extern mi_decl_cache_align const mi_page_t  _mi_page_empty;
+extern mi_decl_thread mi_heap_t*            _mi_heap_default;
 bool       _mi_is_main_thread(void);
 bool       _mi_preloading();  // true while the C runtime is not ready