diff --git a/restricted/types/hashing.go b/restricted/types/hashing.go
index 886d957..fe03ee6 100644
--- a/restricted/types/hashing.go
+++ b/restricted/types/hashing.go
@@ -62,7 +62,7 @@ func prefixedRlpHash(prefix byte, x interface{}) (h core.Hash) {
 // This is internal, do not use.
 type TrieHasher interface {
 	Reset()
-	Update([]byte, []byte)
+	Update([]byte, []byte) error
 	Hash() core.Hash
 }