diff --git a/clang-tools-extra/clang-tidy/add_new_check.py b/clang-tools-extra/clang-tidy/add_new_check.py
--- a/clang-tools-extra/clang-tidy/add_new_check.py
+++ b/clang-tools-extra/clang-tidy/add_new_check.py
@@ -322,8 +322,7 @@
     lines = f.readlines()
   # Get all existing docs
   doc_files = []
-  for subdir in list(filter(lambda s: not s.endswith('.rst') and not s.endswith('.py'),
-                     os.listdir(docs_dir))):
+  for subdir in list(filter(os.path.isdir, os.listdir(docs_dir))):
     for file in filter(lambda s: s.endswith('.rst'), os.listdir(os.path.join(docs_dir, subdir))):
       doc_files.append([subdir, file])
   doc_files.sort()
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -99,6 +99,9 @@
 - Change to Python 3 in the shebang of `add_new_check.py` and `rename_check.py`,
   as the existing code is not compatible with Python 2.
 
+- Fix a minor bug in `add_new_check.py` to only traverse subdirectories
+  when updating the list of checks in the documentation.
+
 New checks
 ^^^^^^^^^^