diff --git a/docs/about/release-notes.md b/docs/about/release-notes.md
index 2af836933c..1d36f4fe58 100644
--- a/docs/about/release-notes.md
+++ b/docs/about/release-notes.md
@@ -56,7 +56,8 @@ your global navigation uses more than one level, things will likely be broken.
 
 ### Other Changes and Additions to Version 1.1
 
-* Bugfix: Exclude Markdown files and READMEs from theme. (#1766).
+* Bugfix: Properly build `ValidationError` message for `custom_dir` (#1849).
+* Bugfix: Exclude Markdown files and READMEs from theme (#1766).
 * Bugfix: Account for encoded URLs (#1670).
 * Bugfix: Ensure theme files do not override `docs_dir` files (#1671).
 * Bugfix: Do not normalize URL fragments (#1655).
diff --git a/mkdocs/config/config_options.py b/mkdocs/config/config_options.py
index e555139374..7012804b34 100644
--- a/mkdocs/config/config_options.py
+++ b/mkdocs/config/config_options.py
@@ -456,7 +456,7 @@ def post_validation(self, config, key_name):
 
         if 'custom_dir' in theme_config and not os.path.isdir(theme_config['custom_dir']):
             raise ValidationError("The path set in {name}.custom_dir ('{path}') does not exist.".
-                                  format(path=theme_config['custom_dir'], name=self.name))
+                                  format(path=theme_config['custom_dir'], name=key_name))
 
         config[key_name] = theme.Theme(**theme_config)