During a recent validate with Sphinx (sphinx-build) 1.3.1 (as packaged by Arch Linux), I got this failure:

reading sources... [ 33%] glasgow_exts                                         
Exception occurred:
  File "/usr/lib/python3.5/site-packages/sphinx/environment.py", line 863, in read_doc
    pickle.dump(doctree, f, pickle.HIGHEST_PROTOCOL)
RecursionError: maximum recursion depth exceeded while pickling an object
The full traceback has been saved in /tmp/sphinx-err-11x82xjc.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
docs/users_guide/ghc.mk:30: recipe for target 'docs/users_guide/ghc.1' failed
make[1]: *** [docs/users_guide/ghc.1] Error 1
Makefile:121: recipe for target 'all' failed
make: *** [all] Error 2

The contents of the referenced log:

# Sphinx version: 1.3.1  
# Python version: 3.5.0 (CPython)  
# Docutils version: 0.12 release  
# Jinja2 version: 2.8  
# Last messages:  
#   reading sources... [  6%] bugs  
#   reading sources... [  9%] codegens  
#   reading sources... [ 12%] debugging  
#   reading sources... [ 15%] editing-guide  
#   reading sources... [ 18%] extending_ghc  
#   reading sources... [ 21%] ffi-chap  
#   reading sources... [ 24%] flags  
#   reading sources... [ 27%] ghc  
#   reading sources... [ 30%] ghci  
#   reading sources... [ 33%] glasgow_exts  
# Loaded extensions:
#   sphinx.ext.extlinks (1.3.1) from /usr/lib/python3.5/site-packages/sphinx/ext/extlinks.py
#   alabaster (0.7.6) from /usr/lib/python3.5/site-packages/alabaster/__init__.py
Traceback (most recent call last):
  File "/usr/lib/python3.5/site-packages/sphinx/cmdline.py", line 245, in main
    app.build(opts.force_all, filenames)
  File "/usr/lib/python3.5/site-packages/sphinx/application.py", line 264, in build
    self.builder.build_update()
  File "/usr/lib/python3.5/site-packages/sphinx/builders/__init__.py", line 240, in build_update
    self.build(['__all__'], to_build)  
  File "/usr/lib/python3.5/site-packages/sphinx/builders/__init__.py", line 259, in build
    self.doctreedir, self.app))  
  File "/usr/lib/python3.5/site-packages/sphinx/environment.py", line 618, in update
    self._read_serial(docnames, app)
  File "/usr/lib/python3.5/site-packages/sphinx/environment.py", line 638, in _read_serial
    self.read_doc(docname, app)
  File "/usr/lib/python3.5/site-packages/sphinx/environment.py", line 863, in read_doc
    pickle.dump(doctree, f, pickle.HIGHEST_PROTOCOL)
RecursionError: maximum recursion depth exceeded while pickling an object