diff --git a/docs/source/changes.md b/docs/source/changes.md
index ab7a8e23..7f826fec 100644
--- a/docs/source/changes.md
+++ b/docs/source/changes.md
@@ -18,6 +18,7 @@ releases are available on [PyPI](https://pypi.org/project/pytask) and
 - {pull}`555` uses new-style hook wrappers and requires pluggy 1.3 for typing.
 - {pull}`557` fixes an issue with `@task(after=...)` in notebooks and terminals.
 - {pull}`566` makes universal-pathlib an official dependency.
+- {pull}`568` restricts `task_files` to a list of patterns and raises a better error.
 
 ## 0.4.5 - 2024-01-09
 
diff --git a/docs/source/reference_guides/configuration.md b/docs/source/reference_guides/configuration.md
index 9564298f..da8ece2b 100644
--- a/docs/source/reference_guides/configuration.md
+++ b/docs/source/reference_guides/configuration.md
@@ -242,7 +242,7 @@ strict_markers = true
 Change the pattern which identify task files.
 
 ```toml
-task_files = "task_*.py"  # default
+task_files = ["task_*.py"]  # default
 
 task_files = ["task_*.py", "tasks_*.py"]
 ```
diff --git a/src/_pytask/build.py b/src/_pytask/build.py
index fe0c2c1e..5c598705 100644
--- a/src/_pytask/build.py
+++ b/src/_pytask/build.py
@@ -95,7 +95,7 @@ def build(  # noqa: C901, PLR0912, PLR0913, PLR0915
     stop_after_first_failure: bool = False,
     strict_markers: bool = False,
     tasks: Callable[..., Any] | PTask | Iterable[Callable[..., Any] | PTask] = (),
-    task_files: str | Iterable[str] = "task_*.py",
+    task_files: Iterable[str] = ("task_*.py",),
     trace: bool = False,
     verbose: int = 1,
     **kwargs: Any,
diff --git a/src/_pytask/config.py b/src/_pytask/config.py
index ac4775da..86423ac3 100644
--- a/src/_pytask/config.py
+++ b/src/_pytask/config.py
@@ -92,7 +92,13 @@ def pytask_parse_config(config: dict[str, Any]) -> None:
         + IGNORED_TEMPORARY_FILES_AND_FOLDERS
     )
 
-    config["task_files"] = to_list(config.get("task_files", "task_*.py"))
+    value = config.get("task_files", ["task_*.py"])
+    if not isinstance(value, (list, tuple)) or not all(
+        isinstance(p, str) for p in value
+    ):
+        msg = "'task_files' must be a list of patterns."
+        raise ValueError(msg)
+    config["task_files"] = value
 
     if config["stop_after_first_failure"]:
         config["max_failures"] = 1
diff --git a/tests/test_collect.py b/tests/test_collect.py
index 5ef6f6c0..d6f3c139 100644
--- a/tests/test_collect.py
+++ b/tests/test_collect.py
@@ -103,10 +103,10 @@ def test_collect_same_task_different_ways(tmp_path, path_extension):
 @pytest.mark.parametrize(
     ("task_files", "pattern", "expected_collected_tasks"),
     [
-        (["example_task.py"], "'*_task.py'", 1),
-        (["tasks_example.py"], "'tasks_*'", 1),
-        (["example_tasks.py"], "'*_tasks.py'", 1),
-        (["task_module.py", "tasks_example.py"], "'tasks_*.py'", 1),
+        (["example_task.py"], "['*_task.py']", 1),
+        (["tasks_example.py"], "['tasks_*']", 1),
+        (["example_tasks.py"], "['*_tasks.py']", 1),
+        (["task_module.py", "tasks_example.py"], "['tasks_*.py']", 1),
         (["task_module.py", "tasks_example.py"], "['task_*.py', 'tasks_*.py']", 2),
     ],
 )
@@ -117,8 +117,8 @@ def test_collect_files_w_custom_file_name_pattern(
         f"[tool.pytask.ini_options]\ntask_files = {pattern}"
     )
 
-    for file in task_files:
-        tmp_path.joinpath(file).write_text("def task_example(): pass")
+    for file_ in task_files:
+        tmp_path.joinpath(file_).write_text("def task_example(): pass")
 
     session = build(paths=tmp_path)
 
@@ -126,6 +126,21 @@ def test_collect_files_w_custom_file_name_pattern(
     assert len(session.tasks) == expected_collected_tasks
 
 
+def test_error_with_invalid_file_name_pattern(runner, tmp_path):
+    tmp_path.joinpath("pyproject.toml").write_text(
+        "[tool.pytask.ini_options]\ntask_files = 'asds'"
+    )
+
+    result = runner.invoke(cli, [tmp_path.as_posix()])
+    assert result.exit_code == ExitCode.CONFIGURATION_FAILED
+    assert "'task_files' must be a list of patterns." in result.output
+
+
+def test_error_with_invalid_file_name_pattern_(tmp_path):
+    session = build(paths=tmp_path, task_files=[1])
+    assert session.exit_code == ExitCode.CONFIGURATION_FAILED
+
+
 @pytest.mark.unit()
 @pytest.mark.parametrize(
     ("session", "path", "node_info", "expected"),