diff --git a/roles/sphinx/README.rst b/roles/sphinx/README.rst
index fcad72530..5a4929260 100644
--- a/roles/sphinx/README.rst
+++ b/roles/sphinx/README.rst
@@ -19,8 +19,10 @@ Run sphinx to generate documentation
 
 .. zuul:rolevar:: sphinx_warning_is_error
 
-   Whether to treat sphinx build warnings as errors. Defaults to undefined
-   which means to attempt to find the setting in a setup.cfg file.
+   Whether to treat sphinx build warnings as errors. Defaults to the value of
+   ``[build_sphinx] warning-is-error`` in ``setup.cfg`` if defined, ``False``
+   if the ``[build_sphinx]`` section is present but the ``warning-is-error``
+   option is undefined, or ``True`` if the entire section is undefined.
 
 .. zuul:rolevar:: zuul_work_virtualenv
    :default: ~/.venv
diff --git a/roles/sphinx/library/sphinx_check_warning_is_error.py b/roles/sphinx/library/sphinx_check_warning_is_error.py
index d067d2017..275d8c0a7 100644
--- a/roles/sphinx/library/sphinx_check_warning_is_error.py
+++ b/roles/sphinx/library/sphinx_check_warning_is_error.py
@@ -68,7 +68,7 @@ def main():
     )
     project_dir = module.params['project_dir']
 
-    warning_is_error = False
+    warning_is_error = True
     # TODO(mordred) Remove autodoc_index_modules logic  when we get OpenStack
     # projects off of the pbr autoindex
     autodoc_index_modules = False
@@ -91,9 +91,11 @@ def main():
             autodoc_index_modules=autodoc_index_modules,
             msg="Error reading setup.cfg, defaulting flags to false")
 
-    if (c.has_section('build_sphinx') and
-            c.has_option('build_sphinx', 'warning-is-error')):
-        warning_is_error = c.getboolean('build_sphinx', 'warning-is-error')
+    if c.has_section('build_sphinx'):
+        if c.has_option('build_sphinx', 'warning-is-error'):
+            warning_is_error = c.getboolean('build_sphinx', 'warning-is-error')
+        else:
+            warning_is_error = False
     if c.has_section('pbr') and c.has_option('pbr', 'autodoc_index_modules'):
         autodoc_index_modules = c.getboolean('pbr', 'autodoc_index_modules')
     if (c.has_section('pbr') and