diff --git a/doc/gendoc.py b/doc/gendoc.py
--- a/doc/gendoc.py
+++ b/doc/gendoc.py
@@ -1,6 +1,8 @@
-import sys, textwrap
+import os, sys, textwrap
 # import from the live mercurial repo
 sys.path.insert(0, "..")
+# fall back to pure modules if required C extensions are not available
+sys.path.append(os.path.join('..', 'mercurial', 'pure'))
 from mercurial import demandimport; demandimport.enable()
 from mercurial.commands import table, globalopts
 from mercurial.i18n import gettext, _