diff --git a/src/name-assignment/assignment-email.cpp b/src/name-assignment/assignment-email.cpp
index 2cb6184..b8f4b5b 100644
--- a/src/name-assignment/assignment-email.cpp
+++ b/src/name-assignment/assignment-email.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2017-2022, Regents of the University of California.
+ * Copyright (c) 2017-2024, Regents of the University of California.
  *
  * This file is part of ndncert, a certificate management system based on NDN.
  *
@@ -47,12 +47,12 @@
           formatIter++;
         }
         else {
-          result.push_back(domain.substr(domainSplit + 1).c_str());
+          result.append(domain.substr(domainSplit + 1).data());
         }
         domain = domain.substr(0, domainSplit);
         domainSplit = domain.rfind(".");
       }
-      result.push_back(email.substr(0, emailSplit).c_str());
+      result.append(email.substr(0, emailSplit).data());
       resultList.push_back(std::move(result));
     }
   }