diff --git a/llvm/cmake/modules/AddSphinxTarget.cmake b/llvm/cmake/modules/AddSphinxTarget.cmake
--- a/llvm/cmake/modules/AddSphinxTarget.cmake
+++ b/llvm/cmake/modules/AddSphinxTarget.cmake
@@ -38,6 +38,7 @@
                             -b ${builder}
                             -d "${SPHINX_DOC_TREE_DIR}"
                             -q # Quiet: no output other than errors and warnings.
+                            -t builder-${builder} # tag for builder
                             ${SPHINX_WARNINGS_AS_ERRORS_FLAG} # Treat warnings as errors if requested
                             "${ARG_SOURCE_DIR}" # Source
                             "${SPHINX_BUILD_DIR}" # Output
diff --git a/llvm/docs/conf.py b/llvm/docs/conf.py
--- a/llvm/docs/conf.py
+++ b/llvm/docs/conf.py
@@ -28,22 +28,29 @@
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 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']
 
 # The suffix of source filenames.
 source_suffix = {
     '.rst': 'restructuredtext',
-    '.md': 'markdown',
 }
 
+try:
+  import recommonmark
+except ImportError:
+  # manpages do not use any .md sources
+  if not tags.has('builder-man'):
+    raise
+else:
+  import sphinx
+  if sphinx.version_info >= (3, 0):
+    # This requires 0.5 or later.
+    extensions.append('recommonmark')
+  else:
+    source_parsers = {'.md': 'recommonmark.parser.CommonMarkParser'}
+  source_suffix['.md'] = 'markdown'
+
 # The encoding of source files.
 #source_encoding = 'utf-8-sig'