diff --git a/doc/extdev/builderapi.rst b/doc/extdev/builderapi.rst
index 0ab7a30f4..5c5a52583 100644
--- a/doc/extdev/builderapi.rst
+++ b/doc/extdev/builderapi.rst
@@ -16,6 +16,7 @@ Builder API
    .. autoattribute:: name
    .. autoattribute:: format
    .. autoattribute:: epilog
+   .. autoattribute:: allow_parallel
    .. autoattribute:: supported_image_types
    .. autoattribute:: supported_remote_images
    .. autoattribute:: supported_data_uri_images
diff --git a/sphinx/builders/__init__.py b/sphinx/builders/__init__.py
index 722f9a280..5ad989539 100644
--- a/sphinx/builders/__init__.py
+++ b/sphinx/builders/__init__.py
@@ -68,7 +68,7 @@ class Builder:
     # doctree versioning method
     versioning_method = 'none'
     versioning_compare = False
-    # allow parallel write_doc() calls
+    #: allow parallel write_doc() calls
     allow_parallel = False
     # support translation
     use_message_catalog = True