diff --git a/sphinx/builders/latex.py b/sphinx/builders/latex.py
index 4e906ea60..c03803c5a 100644
--- a/sphinx/builders/latex.py
+++ b/sphinx/builders/latex.py
@@ -248,14 +248,6 @@ class LaTeXBuilder(Builder):
                                    path.join(self.srcdir, src), err)
 
 
-def validate_config_values(app):
-    # type: (Sphinx) -> None
-    if app.config.latex_toplevel_sectioning not in (None, 'part', 'chapter', 'section'):
-        logger.warning('invalid latex_toplevel_sectioning, ignored: %s',
-                       app.config.latex_toplevel_sectioning)
-        app.config.latex_toplevel_sectioning = None  # type: ignore
-
-
 def default_latex_engine(config):
     # type: (Config) -> unicode
     """ Better default latex_engine settings for specific languages. """
@@ -278,7 +270,6 @@ def default_latex_docclass(config):
 def setup(app):
     # type: (Sphinx) -> Dict[unicode, Any]
     app.add_builder(LaTeXBuilder)
-    app.connect('builder-inited', validate_config_values)
 
     app.add_config_value('latex_engine', default_latex_engine, None,
                          ENUM('pdflatex', 'xelatex', 'lualatex', 'platex'))
@@ -289,7 +280,8 @@ def setup(app):
     app.add_config_value('latex_logo', None, None, string_classes)
     app.add_config_value('latex_appendices', [], None)
     app.add_config_value('latex_use_latex_multicolumn', False, None)
-    app.add_config_value('latex_toplevel_sectioning', None, None, [str])
+    app.add_config_value('latex_toplevel_sectioning', None, None,
+                         ENUM('part', 'chapter', 'section'))
     app.add_config_value('latex_domain_indices', True, None, [list])
     app.add_config_value('latex_show_urls', 'no', None)
     app.add_config_value('latex_show_pagerefs', False, None)