diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -1291,6 +1291,10 @@ Controls generic server settings.
     checking that all new file revisions specified in manifests are
     present. Default is False.
 
+``maxhttpheaderlen``
+    Instruct HTTP clients not to send request headers longer than this
+    many bytes. Default is 1024.
+
 ``smtp``
 --------
 
diff --git a/mercurial/wireproto.py b/mercurial/wireproto.py
--- a/mercurial/wireproto.py
+++ b/mercurial/wireproto.py
@@ -624,7 +624,8 @@ def _capabilities(repo, proto):
         capsblob = bundle2.encodecaps(bundle2.getrepocaps(repo))
         caps.append('bundle2=' + urllib.quote(capsblob))
     caps.append('unbundle=%s' % ','.join(changegroupmod.bundlepriority))
-    caps.append('httpheader=1024')
+    caps.append(
+        'httpheader=%d' % repo.ui.configint('server', 'maxhttpheaderlen', 1024))
     return caps
 
 # If you are writing an extension and consider wrapping this function. Wrap