Index: llvm/docs/conf.py
===================================================================
--- llvm/docs/conf.py
+++ llvm/docs/conf.py
@@ -26,7 +26,14 @@
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = ['sphinx.ext.intersphinx', 'sphinx.ext.todo', 'recommonmark']
+extensions = ['sphinx.ext.intersphinx', 'sphinx.ext.todo']
+
+import sphinx
+if sphinx.version_info >= (3, 0):
+  # This requires 0.5 or later.
+  extensions.append('recommonmark')
+else:
+  source_parsers = {'.md': 'recommonmark.parser.CommonMarkParser'}
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']