diff --git a/fix_future_annotations/_main.py b/fix_future_annotations/_main.py
index 65816e8..71fa903 100644
--- a/fix_future_annotations/_main.py
+++ b/fix_future_annotations/_main.py
@@ -4,7 +4,9 @@
 import ast
 import difflib
 import sys
+import os
 from pathlib import Path
+from typing import Iterator
 
 from tokenize_rt import reversed_enumerate, src_to_tokens, tokens_to_src
 
@@ -15,6 +17,20 @@ def _escaped(line: str) -> bool:
     return (len(line) - len(line.rstrip("\\"))) % 2 == 1
 
 
+def _iter_files(*paths: str) -> Iterator[str]:
+    def files_under_dir(path: str) -> Iterator[str]:
+        for root, _, files in os.walk(path):
+            for filename in files:
+                if filename.endswith(".py"):
+                    yield os.path.join(root, filename)
+
+    for path in paths:
+        if os.path.isdir(path):
+            yield from files_under_dir(path)
+        elif path.endswith(".py"):
+            yield path
+
+
 def _add_future_annotations(content: str) -> str:
     """Add from __future__ annotations after the first docstring and comments"""
     new_lines = ["from __future__ import annotations\n"]
@@ -106,7 +122,7 @@ def fix_file(
 
 def main(argv: list[str] | None = None) -> None:
     parser = argparse.ArgumentParser()
-    parser.add_argument("filenames", nargs="+", help="File(s) to fix")
+    parser.add_argument("path", nargs="+", help="File or directory path(s) to fix")
     parser.add_argument(
         "--check",
         "-c",
@@ -120,16 +136,18 @@ def main(argv: list[str] | None = None) -> None:
     )
     args = parser.parse_args(argv)
     diff_count = 0
-    for filename in args.filenames:
-        if filename.endswith(".py"):
-            result = fix_file(filename, args.write, show_diff=args.verbose)
-            diff_count += int(result)
+    checked = 0
+    for filename in _iter_files(*args.path):
+        checked += 1
+        result = fix_file(filename, args.write, show_diff=args.verbose)
+        diff_count += int(result)
     if diff_count:
         if args.write:
             message = f"All complete, {diff_count} files were fixed"
         else:
             message = f"All complete, {diff_count} files need to be fixed"
-        print(message)
+        if checked > 1:  # multiple mode, print a summary
+            print(message)
         sys.exit(1)
-    else:
+    elif checked > 1:
         print("All complete, no file is changed")