1 files changed, 3 insertions, 3 deletions
diff --git a/upb/upb.c b/upb/upb.c
index d8d2723..9f80639 100644
--- a/upb/upb.c
+++ b/upb/upb.c
@@ -191,10 +191,8 @@ upb_arena *upb_arena_init(void *mem, size_t n, upb_alloc *alloc) {
     }
   }
 
-  a = mem;
-  mem = (char*)mem + sizeof(*a);
+  a = (void*)((char*)mem + n - sizeof(*a));
   n -= sizeof(*a);
-  upb_arena_addblock(a, mem, n, owned);
 
   a->alloc.func = &upb_arena_doalloc;
   a->block_alloc = &upb_alloc_global;
@@ -205,6 +203,8 @@ upb_arena *upb_arena_init(void *mem, size_t n, upb_alloc *alloc) {
   a->block_head = NULL;
   a->block_alloc = alloc;
 
+  upb_arena_addblock(a, mem, n, owned);
+
   return a;
 }