diff --git a/aider/commands.py b/aider/commands.py
index e2070e049..b09fe1a5d 100644
--- a/aider/commands.py
+++ b/aider/commands.py
@@ -238,6 +238,7 @@ class Commands:
         git_added = []
         git_files = self.coder.get_tracked_files()
 
+        expanded_files = set()
         for word in args.split():
             matched_files = self.glob_filtered_to_repo(word)
 
@@ -246,42 +247,36 @@ class Commands:
                     self.io.tool_error(f"No files to add matching pattern: {word}")
                 else:
                     if Path(word).exists():
-                        if Path(word).is_file():
-                            matched_files = [word]
-                        elif Path(word).is_dir():
-                            matched_files = expand_subdir(word)
-                        else:
-                            self.io.tool_error(f"Can not add unknown file type: {word}")
+                        matched_files = [word]
                     elif self.io.confirm_ask(
                         f"No files matched '{word}'. Do you want to create the file?"
                     ):
                         (Path(self.coder.root) / word).touch()
                         matched_files = [word]
 
-            expanded_files = []
             for matched_file in matched_files:
                 if Path(matched_file).is_dir():
-                    expanded_files += expand_subdir(matched_file)
+                    expanded_files.update(expand_subdir(matched_file))
                 else:
-                    expanded_files.append(matched_file)
+                    expanded_files.add(matched_file)
 
-            for matched_file in expanded_files:
-                abs_file_path = self.coder.abs_root_path(matched_file)
+        for matched_file in expanded_files:
+            abs_file_path = self.coder.abs_root_path(matched_file)
 
-                if self.coder.repo and matched_file not in git_files:
-                    self.coder.repo.git.add(abs_file_path)
-                    git_added.append(matched_file)
+            if self.coder.repo and matched_file not in git_files:
+                self.coder.repo.git.add(abs_file_path)
+                git_added.append(matched_file)
 
-                if abs_file_path not in self.coder.abs_fnames:
-                    content = self.io.read_text(abs_file_path)
-                    if content is not None:
-                        self.coder.abs_fnames.add(abs_file_path)
-                        self.io.tool_output(f"Added {matched_file} to the chat")
-                        added_fnames.append(matched_file)
-                    else:
-                        self.io.tool_error(f"Unable to read {matched_file}")
+            if abs_file_path not in self.coder.abs_fnames:
+                content = self.io.read_text(abs_file_path)
+                if content is not None:
+                    self.coder.abs_fnames.add(abs_file_path)
+                    self.io.tool_output(f"Added {matched_file} to the chat")
+                    added_fnames.append(matched_file)
                 else:
-                    self.io.tool_error(f"{matched_file} is already in the chat")
+                    self.io.tool_error(f"Unable to read {matched_file}")
+            else:
+                self.io.tool_error(f"{matched_file} is already in the chat")
 
         if self.coder.repo and git_added:
             git_added = " ".join(git_added)
diff --git a/tests/test_commands.py b/tests/test_commands.py
index 3a2749122..642b4e561 100644
--- a/tests/test_commands.py
+++ b/tests/test_commands.py
@@ -89,17 +89,21 @@ class TestCommands(TestCase):
 
         # Create a directory and add files to it
         os.mkdir("test_dir")
+        os.mkdir("test_dir/another_dir")
         with open("test_dir/test_file1.txt", "w") as f:
             f.write("Test file 1")
         with open("test_dir/test_file2.txt", "w") as f:
             f.write("Test file 2")
+        with open("test_dir/another_dir/test_file.txt", "w") as f:
+            f.write("Test file 3")
 
         # Call the cmd_add method with a directory
-        commands.cmd_add("test_dir")
+        commands.cmd_add("test_dir test_dir/test_file2.txt")
 
         # Check if the files have been added to the chat session
         self.assertIn(str(Path("test_dir/test_file1.txt").resolve()), coder.abs_fnames)
         self.assertIn(str(Path("test_dir/test_file2.txt").resolve()), coder.abs_fnames)
+        self.assertIn(str(Path("test_dir/another_dir/test_file.txt").resolve()), coder.abs_fnames)
 
     def test_cmd_drop_with_glob_patterns(self):
         # Initialize the Commands and InputOutput objects