diff --git a/vcsserver/scm_app.py b/vcsserver/scm_app.py
--- a/vcsserver/scm_app.py
+++ b/vcsserver/scm_app.py
@@ -136,6 +136,9 @@ def make_hg_ui_from_config(repo_config):
     # make our hgweb quiet so it doesn't print output
     baseui.setconfig(b'ui', b'quiet', b'true')
 
+    # use POST requests with args instead of GET with headers - fixes issues with big repos with lots of branches
+    baseui.setconfig(b'experimental', b'httppostargs', b'true')
+
     return baseui