diff --git a/env/io_posix.h b/env/io_posix.h
index 606e932bb57661014e3c6d97f8d88af0b49e6ebb..65c74758c9560b5155a7c5852664e5e11328909d 100644
--- a/env/io_posix.h
+++ b/env/io_posix.h
@@ -97,6 +97,9 @@ inline void UpdateResult(struct io_uring_cqe* cqe, const std::string& file_name,
                             cqe->res);
     }
   }
+#ifdef NDEBUG
+  (void)len;
+#endif
 }
 #endif