diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 3045be5..c71b841 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -56,4 +56,7 @@ repos:
               [.]pre-commit-config[.]yaml$|
               [.]pre-commit-hooks[.]yaml$|
               pyproject[.]toml$
+        exclude: |
+          (?x)
+              test_copyright[.]py$
         args: [--fix, --main-branch=main]
diff --git a/src/rapids_pre_commit_hooks/copyright.py b/src/rapids_pre_commit_hooks/copyright.py
index 232afe5..e93470b 100644
--- a/src/rapids_pre_commit_hooks/copyright.py
+++ b/src/rapids_pre_commit_hooks/copyright.py
@@ -231,18 +231,20 @@ def get_changed_files(args):
         changed_files.update({blob.path: None for _, blob in repo.index.iter_blobs()})
         return changed_files
 
-    diffs = target_branch_upstream_commit.diff(
-        other=None,
-        merge_base=True,
-        find_copies=True,
-        find_copies_harder=True,
-        find_renames=True,
-    )
-    for diff in diffs:
-        if diff.change_type == "A":
-            changed_files[diff.b_path] = None
-        elif diff.change_type != "D":
-            changed_files[diff.b_path] = diff.a_blob
+    for merge_base in repo.merge_base(
+        repo.head.commit, target_branch_upstream_commit, all=True
+    ):
+        diffs = merge_base.diff(
+            other=None,
+            find_copies=True,
+            find_copies_harder=True,
+            find_renames=True,
+        )
+        for diff in diffs:
+            if diff.change_type == "A":
+                changed_files[diff.b_path] = None
+            elif diff.change_type != "D":
+                changed_files[diff.b_path] = diff.a_blob
 
     return changed_files
 
diff --git a/test/rapids_pre_commit_hooks/test_copyright.py b/test/rapids_pre_commit_hooks/test_copyright.py
index 166d169..884b21c 100644
--- a/test/rapids_pre_commit_hooks/test_copyright.py
+++ b/test/rapids_pre_commit_hooks/test_copyright.py
@@ -649,6 +649,85 @@ def file_contents(verbed):
             assert changed_files[new].data_stream.read() == old_contents
 
 
+def test_get_changed_files_multiple_merge_bases(git_repo):
+    def fn(filename):
+        return os.path.join(git_repo.working_tree_dir, filename)
+
+    def write_file(filename, contents):
+        with open(fn(filename), "w") as f:
+            f.write(contents)
+
+    write_file("file1.txt", "File 1\n")
+    write_file("file2.txt", "File 2\n")
+    write_file("file3.txt", "File 3\n")
+    git_repo.index.add(["file1.txt", "file2.txt", "file3.txt"])
+    git_repo.index.commit("Initial commit")
+
+    branch_1 = git_repo.create_head("branch-1", "master")
+    git_repo.head.reference = branch_1
+    git_repo.index.reset(index=True, working_tree=True)
+    write_file("file1.txt", "File 1 modified\n")
+    git_repo.index.add("file1.txt")
+    git_repo.index.commit(
+        "Modify file1.txt",
+        commit_date=datetime.datetime(2024, 1, 1, tzinfo=datetime.timezone.utc),
+    )
+
+    branch_2 = git_repo.create_head("branch-2", "master")
+    git_repo.head.reference = branch_2
+    git_repo.index.reset(index=True, working_tree=True)
+    write_file("file2.txt", "File 2 modified\n")
+    git_repo.index.add("file2.txt")
+    git_repo.index.commit(
+        "Modify file2.txt",
+        commit_date=datetime.datetime(2024, 2, 1, tzinfo=datetime.timezone.utc),
+    )
+
+    branch_1_2 = git_repo.create_head("branch-1-2", "master")
+    git_repo.head.reference = branch_1_2
+    git_repo.index.reset(index=True, working_tree=True)
+    write_file("file1.txt", "File 1 modified\n")
+    write_file("file2.txt", "File 2 modified\n")
+    git_repo.index.add(["file1.txt", "file2.txt"])
+    git_repo.index.commit(
+        "Merge branches branch-1 and branch-2",
+        parent_commits=[branch_1.commit, branch_2.commit],
+        commit_date=datetime.datetime(2024, 3, 1, tzinfo=datetime.timezone.utc),
+    )
+
+    branch_3 = git_repo.create_head("branch-3", "master")
+    git_repo.head.reference = branch_3
+    git_repo.index.reset(index=True, working_tree=True)
+    write_file("file1.txt", "File 1 modified\n")
+    write_file("file2.txt", "File 2 modified\n")
+    git_repo.index.add(["file1.txt", "file2.txt"])
+    git_repo.index.commit(
+        "Merge branches branch-1 and branch-2",
+        parent_commits=[branch_1.commit, branch_2.commit],
+        commit_date=datetime.datetime(2024, 4, 1, tzinfo=datetime.timezone.utc),
+    )
+    write_file("file3.txt", "File 3 modified\n")
+    git_repo.index.add("file3.txt")
+    git_repo.index.commit(
+        "Modify file3.txt",
+        commit_date=datetime.datetime(2024, 5, 1, tzinfo=datetime.timezone.utc),
+    )
+
+    with patch("os.getcwd", Mock(return_value=git_repo.working_tree_dir)), patch(
+        "rapids_pre_commit_hooks.copyright.get_target_branch",
+        Mock(return_value="branch-1-2"),
+    ):
+        changed_files = copyright.get_changed_files(None)
+    assert {
+        path: old_blob.path if old_blob else None
+        for path, old_blob in changed_files.items()
+    } == {
+        "file1.txt": "file1.txt",
+        "file2.txt": "file2.txt",
+        "file3.txt": "file3.txt",
+    }
+
+
 def test_normalize_git_filename():
     assert copyright.normalize_git_filename("file.txt") == "file.txt"
     assert copyright.normalize_git_filename("sub/file.txt") == "sub/file.txt"