# must fail: head_proof_ok_O3
# the root merge drops the ROOT flag (head_proof::merge_root)
diff --git a/wai/wai-rs/src/http_binding/head_proof.rs b/wai/wai-rs/src/http_binding/head_proof.rs
index 40b6f1fa..69ba8a98 100644
--- a/wai/wai-rs/src/http_binding/head_proof.rs
+++ b/wai/wai-rs/src/http_binding/head_proof.rs
@@ -40,7 +40,7 @@ fn left_len(n: u64) -> u64 {
 
 /// The root of a tree from its two children: BLAKE3's parent node with the ROOT flag.
 fn merge_root(l: &ChainingValue, r: &ChainingValue) -> [u8; 32] {
-    *merge_subtrees_root(l, r, Mode::Hash).as_bytes()
+    merge_subtrees_non_root(l, r, Mode::Hash)
 }
 
 /// The non-root chaining value of the subtree `x[..len]` whose first chunk is at