@@ -221,7 +221,9 @@ def git_create_branch(
 
     # GitPython's create_head accepts a name that already points at the base
     # commit, so check first rather than report a branch that was not created.
-    if branch_name in repo.heads:
+    # Compare names: `in repo.heads` also matches IterableList attributes
+    # such as "append".
+    if any(head.name == branch_name for head in repo.heads):
         raise ValueError(
             f"Cannot create branch '{branch_name}': refs/heads/{branch_name} already exists"
         )
 
@@ -617,6 +617,17 @@ async def test_git_create_branch_existing_name_at_same_commit_is_error(
     )
 
 
+async def test_git_create_branch_name_matching_list_attribute(repo: git.Repo):
+    # The existence check compares head names, so a new branch named like an
+    # attribute of GitPython's IterableList ("append") is still created.
+    assert await call(
+        None,
+        "git_create_branch",
+        {"repo_path": str(root_of(repo)), "branch_name": "append"},
+    ) == text_result("Created branch 'append' from 'main'")
+    assert repo.commit("refs/heads/append") == repo.heads["main"].commit
+
+
 async def test_git_create_branch_existing_name_at_other_commit_is_error(
     repo: git.Repo,
 ):