diff --git a/aider/repo.py b/aider/repo.py
index 28b3c700d..040f8156b 100644
--- a/aider/repo.py
+++ b/aider/repo.py
@@ -126,13 +126,35 @@ class GitRepo:
         return commit_message
 
     def get_diffs(self, pretty, *args):
-        # we always want diffs of working-dir + index versus repo
-        args = ["--cached"] + list(args)
+        args = list(args)
+
+        # if args are specified, just add --pretty if needed
+        if args:
+            if pretty:
+                args = ["--color"] + args
+            return self.repo.git.diff(*args)
+
+        # otherwise, we always want diffs of index and working dir
+
+        try:
+            commits = self.repo.iter_commits(self.repo.active_branch)
+            current_branch_has_commits = any(commits)
+        except git.exc.GitCommandError:
+            current_branch_has_commits = False
 
         if pretty:
-            args = ["--color"] + list(args)
+            args = ["--color"]
+
+        if current_branch_has_commits:
+            # if there is a HEAD, just diff against it to pick up index + working
+            args += ["HEAD"]
+            return self.repo.git.diff(*args)
+
+        # diffs in the index
+        diffs = self.repo.git.diff(*(args + ["--cached"]))
+        # plus, diffs in the working dir
+        diffs += self.repo.git.diff(*args)
 
-        diffs = self.repo.git.diff(*args)
         return diffs
 
     def show_diffs(self, pretty):
diff --git a/tests/test_repo.py b/tests/test_repo.py
index df2fdceaa..8451ec309 100644
--- a/tests/test_repo.py
+++ b/tests/test_repo.py
@@ -16,15 +16,60 @@ class TestRepo(unittest.TestCase):
     def test_diffs_empty_repo(self):
         with GitTemporaryDirectory():
             repo = git.Repo()
-            fname = Path("foo.txt")
-            fname.touch()
 
+            # Add a change to the index
+            fname = Path("foo.txt")
+            fname.write_text("index\n")
             repo.git.add(str(fname))
 
+            # Make a change in the working dir
+            fname.write_text("workingdir\n")
+
             git_repo = GitRepo(InputOutput(), None, ".")
             diffs = git_repo.get_diffs(False)
-            self.assertNotEqual(diffs, "")
-            self.assertIsNotNone(diffs)
+            self.assertIn("index", diffs)
+            self.assertIn("workingdir", diffs)
+
+    def test_diffs_nonempty_repo(self):
+        with GitTemporaryDirectory():
+            repo = git.Repo()
+            fname = Path("foo.txt")
+            fname.touch()
+            repo.git.add(str(fname))
+
+            fname2 = Path("bar.txt")
+            fname2.touch()
+            repo.git.add(str(fname2))
+
+            repo.git.commit("-m", "initial")
+
+            fname.write_text("index\n")
+            repo.git.add(str(fname))
+
+            fname2.write_text("workingdir\n")
+
+            git_repo = GitRepo(InputOutput(), None, ".")
+            diffs = git_repo.get_diffs(False)
+            self.assertIn("index", diffs)
+            self.assertIn("workingdir", diffs)
+
+    def test_diffs_between_commits(self):
+        with GitTemporaryDirectory():
+            repo = git.Repo()
+            fname = Path("foo.txt")
+
+            fname.write_text("one\n")
+            repo.git.add(str(fname))
+            repo.git.commit("-m", "initial")
+
+            fname.write_text("two\n")
+            repo.git.add(str(fname))
+            repo.git.commit("-m", "second")
+
+            git_repo = GitRepo(InputOutput(), None, ".")
+            diffs = git_repo.get_diffs(False, ["HEAD~1", "HEAD"])
+            dump(diffs)
+            self.assertIn("two", diffs)
 
     @patch("aider.repo.simple_send_with_retries")
     def test_get_commit_message(self, mock_send):