diff --git a/include/mimalloc/internal.h b/include/mimalloc/internal.h
index f07f2830..a4495c16 100644
--- a/include/mimalloc/internal.h
+++ b/include/mimalloc/internal.h
@@ -115,7 +115,8 @@ mi_arena_id_t _mi_arena_id_none(void);
 void       _mi_arena_free(void* p, size_t size, size_t alignment, size_t align_offset, size_t memid, bool all_committed, mi_stats_t* stats);
 void*      _mi_arena_alloc(size_t size, bool* commit, bool* large, bool* is_pinned, bool* is_zero, mi_arena_id_t req_arena_id, size_t* memid, mi_os_tld_t* tld);
 void*      _mi_arena_alloc_aligned(size_t size, size_t alignment, size_t align_offset, bool* commit, bool* large, bool* is_pinned, bool* is_zero, mi_arena_id_t req_arena_id, size_t* memid, mi_os_tld_t* tld);
-bool       _mi_arena_memid_is_suitable(size_t memid, mi_arena_id_t req_arena_id);
+bool       _mi_arena_memid_is_suitable(size_t arena_memid, mi_arena_id_t request_arena_id);
+bool       _mi_arena_is_os_allocated(size_t arena_memid);
 
 // "segment-cache.c"
 void*      _mi_segment_cache_pop(size_t size, mi_commit_mask_t* commit_mask, mi_commit_mask_t* decommit_mask, bool large_allowed, bool* large, bool* is_pinned, bool* is_zero, mi_arena_id_t req_arena_id, size_t* memid, mi_os_tld_t* tld);
diff --git a/src/arena.c b/src/arena.c
index 18e3f2ac..43defe00 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -117,6 +117,10 @@ bool _mi_arena_memid_is_suitable(size_t arena_memid, mi_arena_id_t request_arena
   return mi_arena_id_is_suitable(id, exclusive, request_arena_id);
 }
 
+bool _mi_arena_is_os_allocated(size_t arena_memid) {
+  return (arena_memid == MI_MEMID_OS);
+}
+
 static size_t mi_block_count_of_size(size_t size) {
   return _mi_divide_up(size, MI_ARENA_BLOCK_SIZE);
 }