diff --git a/archivebox/config.py b/archivebox/config.py
index abc83f79..74e7ee58 100644
--- a/archivebox/config.py
+++ b/archivebox/config.py
@@ -142,9 +142,10 @@ CONFIG_SCHEMA: Dict[str, ConfigDefaultDict] = {
         'CHECK_SSL_VALIDITY':       {'type': bool,  'default': True},
         'MEDIA_MAX_SIZE':           {'type': str,   'default': '750m'},
 
-        'CURL_USER_AGENT':          {'type': str,   'default': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 ArchiveBox/{VERSION} (+https://github.com/ArchiveBox/ArchiveBox/) curl/{CURL_VERSION}'},
-        'WGET_USER_AGENT':          {'type': str,   'default': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 ArchiveBox/{VERSION} (+https://github.com/ArchiveBox/ArchiveBox/) wget/{WGET_VERSION}'},
-        'CHROME_USER_AGENT':        {'type': str,   'default': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 ArchiveBox/{VERSION} (+https://github.com/ArchiveBox/ArchiveBox/)'},
+        'USER_AGENT':               {'type': str,   'default': None},
+        'CURL_USER_AGENT':          {'type': str,   'default': lambda c: c['USER_AGENT'] or 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 ArchiveBox/{VERSION} (+https://github.com/ArchiveBox/ArchiveBox/) curl/{CURL_VERSION}'},
+        'WGET_USER_AGENT':          {'type': str,   'default': lambda c: c['USER_AGENT'] or 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 ArchiveBox/{VERSION} (+https://github.com/ArchiveBox/ArchiveBox/) wget/{WGET_VERSION}'},
+        'CHROME_USER_AGENT':        {'type': str,   'default': lambda c: c['USER_AGENT'] or 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 ArchiveBox/{VERSION} (+https://github.com/ArchiveBox/ArchiveBox/)'},
 
         'COOKIES_FILE':             {'type': str,   'default': None},
         'CHROME_USER_DATA_DIR':     {'type': str,   'default': None},