diff --git a/bin/nn b/bin/nn
index 044b559..1c4b140 100755
--- a/bin/nn
+++ b/bin/nn
@@ -26,6 +26,9 @@ TELEGRAM_PATTERN = re.compile(
 
 NORMALIZED = re.compile(r'^\d{4}-\d{2}-\d{2} .+')
 
+# Windows hidden-file attribute, mirrored from the stat module.
+FILE_ATTRIBUTE_HIDDEN = 0x2
+
 STATUS_RENAME = 'rename'
 STATUS_ALREADY = 'skip (already normalized)'
 STATUS_NO_MATCH = 'skip (no rule matched)'
@@ -148,7 +151,19 @@ def get_date_for_file(filepath, parse_mode):
     return None
 
 
-def collect_files(paths):
+def is_hidden(filepath):
+    """Check whether a file is hidden (dotfile, or hidden attribute on Windows)."""
+    if filepath.name.startswith('.'):
+        return True
+
+    try:
+        attrs = filepath.stat().st_file_attributes
+    except (AttributeError, OSError):
+        return False
+    return bool(attrs & FILE_ATTRIBUTE_HIDDEN)
+
+
+def collect_files(paths, include_hidden=False):
     """Resolve the list of files to process."""
     if not paths:
         paths = ['.']
@@ -157,8 +172,12 @@ def collect_files(paths):
     for path in paths:
         candidate = Path(path)
         if candidate.is_dir():
-            files.extend(sorted(file for file in candidate.iterdir() if file.is_file()))
+            files.extend(sorted(
+                file for file in candidate.iterdir()
+                if file.is_file() and (include_hidden or not is_hidden(file))
+            ))
         elif candidate.is_file():
+            # Explicitly named files are always processed.
             files.append(candidate)
     return files
 
@@ -318,6 +337,12 @@ def main():
         action='store_true',
         help='Force numbering even for already-normalized files (used with -n).',
     )
+    parser.add_argument(
+        '-a',
+        '--all',
+        action='store_true',
+        help='Include hidden files when scanning directories.',
+    )
     parser.add_argument(
         'files',
         nargs='*',
@@ -326,7 +351,7 @@ def main():
 
     args = parser.parse_args()
 
-    files = collect_files(args.files)
+    files = collect_files(args.files, args.all)
     if not files:
         print('No files found.')
         sys.exit(0)