diff --git a/CHANGES b/CHANGES
index 11f62c501..cb94800ec 100644
--- a/CHANGES
+++ b/CHANGES
@@ -36,6 +36,7 @@ Deprecated
 * ``Config.__init__()`` has changed;  the *dirname*, *filename* and *tags*
   argument has been deprecated
 * ``Config.check_types()`` is deprecated
+* ``Config.check_unicode()`` is deprecated
 
 For more details, see `deprecation APIs list
 <http://www.sphinx-doc.org/en/master/extdev/index.html#deprecated-apis>`_
diff --git a/doc/extdev/index.rst b/doc/extdev/index.rst
index bc79394cc..192f6891a 100644
--- a/doc/extdev/index.rst
+++ b/doc/extdev/index.rst
@@ -113,6 +113,11 @@ The following is a list of deprecated interface.
      - (will be) Removed
      - Alternatives
 
+   * - ``Config.check_unicode()``
+     - 1.8
+     - 3.0
+     - ``sphinx.config.check_unicode()``
+
    * - ``Config.check_types()``
      - 1.8
      - 3.0
diff --git a/sphinx/application.py b/sphinx/application.py
index 91302e6e0..eaa5f8ccd 100644
--- a/sphinx/application.py
+++ b/sphinx/application.py
@@ -26,7 +26,7 @@ from six.moves import cStringIO
 
 import sphinx
 from sphinx import package_dir, locale
-from sphinx.config import Config
+from sphinx.config import Config, check_unicode
 from sphinx.deprecation import RemovedInSphinx20Warning, RemovedInSphinx30Warning
 from sphinx.environment import BuildEnvironment
 from sphinx.errors import ApplicationError, ConfigError, VersionRequirementError
@@ -190,8 +190,7 @@ class Sphinx(object):
         else:
             self.config = Config.read(path.join(self.confdir, CONFIG_FILENAME),
                                       confoverrides or {}, self.tags)
-            self.config.check_unicode()
-            # defer checking types until i18n has been initialized
+            check_unicode(self.config)
 
         # initialize some limited config variables before initialize i18n and loading
         # extensions
diff --git a/sphinx/config.py b/sphinx/config.py
index 4e6585334..d1ef82ee4 100644
--- a/sphinx/config.py
+++ b/sphinx/config.py
@@ -34,7 +34,6 @@ if False:
 
 logger = logging.getLogger(__name__)
 
-nonascii_re = re.compile(br'[\x80-\xff]')
 copyright_year_re = re.compile(r'^((\d{4}-)?)(\d{4})(?=[ ,])')
 
 if PY3:
@@ -196,13 +195,9 @@ class Config(object):
 
     def check_unicode(self):
         # type: () -> None
-        # check all string values for non-ASCII characters in bytestrings,
-        # since that can result in UnicodeErrors all over the place
-        for name, value in iteritems(self._raw_config):
-            if isinstance(value, binary_type) and nonascii_re.search(value):
-                logger.warning(__('the config value %r is set to a string with non-ASCII '
-                                  'characters; this can lead to Unicode errors occurring. '
-                                  'Please use Unicode strings, e.g. %r.'), name, u'Content')
+        warnings.warn('Config.check_unicode() is deprecated. Use check_unicode() instead.',
+                      RemovedInSphinx30Warning)
+        check_unicode(self)
 
     def convert_overrides(self, name, value):
         # type: (unicode, Any) -> Any
@@ -434,6 +429,20 @@ def check_confval_types(app, config):
                                           default=type(default)))
 
 
+def check_unicode(config):
+    # type: (Config) -> None
+    """check all string values for non-ASCII characters in bytestrings,
+    since that can result in UnicodeErrors all over the place
+    """
+    nonascii_re = re.compile(br'[\x80-\xff]')
+
+    for name, value in iteritems(config._raw_config):
+        if isinstance(value, binary_type) and nonascii_re.search(value):
+            logger.warning(__('the config value %r is set to a string with non-ASCII '
+                              'characters; this can lead to Unicode errors occurring. '
+                              'Please use Unicode strings, e.g. %r.'), name, u'Content')
+
+
 def setup(app):
     # type: (Sphinx) -> Dict[unicode, Any]
     app.connect('config-inited', convert_source_suffix)