diff --git a/aider/args.py b/aider/args.py
index 60e189706..6df19778b 100644
--- a/aider/args.py
+++ b/aider/args.py
@@ -18,6 +18,15 @@ from aider.deprecated import add_deprecated_model_args
 from .dump import dump  # noqa: F401
 
 
+def resolve_aiderignore_path(path_str, git_root=None):
+    path = Path(path_str)
+    if path.is_absolute():
+        return str(path)
+    elif git_root:
+        return str(Path(git_root) / path)
+    return str(path)
+
+
 def default_env_file(git_root):
     return os.path.join(git_root, ".env") if git_root else ".env"
 
@@ -390,18 +399,10 @@ def get_parser(default_config_files, git_root):
         os.path.join(git_root, ".aiderignore") if git_root else ".aiderignore"
     )
 
-    def resolve_aiderignore_path(path_str):
-        path = Path(path_str)
-        if path.is_absolute():
-            return str(path)
-        elif git_root:
-            return str(Path(git_root) / path)
-        return str(path)
-
     group.add_argument(
         "--aiderignore",
         metavar="AIDERIGNORE",
-        type=resolve_aiderignore_path,
+        type=lambda path_str: resolve_aiderignore_path(path_str, git_root),
         default=default_aiderignore_file,
         help="Specify the aider ignore file (default: .aiderignore in git root)",
     )
diff --git a/tests/basic/test_main.py b/tests/basic/test_main.py
index f5d147c0e..10861abfa 100644
--- a/tests/basic/test_main.py
+++ b/tests/basic/test_main.py
@@ -927,6 +927,27 @@ class TestMain(TestCase):
             repo = git.Repo(git_dir)  # Re-open repo to ensure we get fresh config
             self.assertEqual(repo.git.config("user.name"), "Directive User")
             self.assertEqual(repo.git.config("user.email"), "directive@example.com")
+            
+    def test_resolve_aiderignore_path(self):
+        # Import the function directly to test it
+        from aider.args import resolve_aiderignore_path
+        
+        # Test with absolute path
+        abs_path = os.path.abspath("/tmp/test/.aiderignore")
+        self.assertEqual(resolve_aiderignore_path(abs_path), abs_path)
+        
+        # Test with relative path and git root
+        git_root = "/path/to/git/root"
+        rel_path = ".aiderignore"
+        expected = os.path.join(git_root, rel_path)
+        self.assertEqual(
+            resolve_aiderignore_path(rel_path, git_root), 
+            str(Path(git_root) / rel_path)
+        )
+        
+        # Test with relative path and no git root
+        rel_path = ".aiderignore"
+        self.assertEqual(resolve_aiderignore_path(rel_path), rel_path)
 
     def test_invalid_edit_format(self):
         with GitTemporaryDirectory():