1 files changed, 1 insertions, 1 deletions
diff --git a/zix/tree.h b/zix/tree.h
index b54087c..87a6c25 100644
--- a/zix/tree.h
+++ b/zix/tree.h
@@ -64,7 +64,7 @@ zix_tree_free(ZixTree* t);
 */
 ZIX_API
 size_t
-zix_tree_size(ZixTree* t);
+zix_tree_size(const ZixTree* t);
 
 /**
    Insert the element @a e into @a t and point @a ti at the new element.