diff --git a/hokusai/builder.py b/hokusai/builder.py
index 087e1f9..322632f 100644
--- a/hokusai/builder.py
+++ b/hokusai/builder.py
@@ -91,9 +91,9 @@ def _collect_extra_params(target_name: str, config: ProjectConfig) -> dict[str,
     if target_cfg.height is not None:
         params["height"] = target_cfg.height
     if target_cfg.reference_images:
-        params["reference_images"] = tuple(target_cfg.reference_images)
+        params["reference_images"] = list(target_cfg.reference_images)
     if target_cfg.control_images:
-        params["control_images"] = tuple(target_cfg.control_images)
+        params["control_images"] = list(target_cfg.control_images)
     return params
 
 
diff --git a/tests/test_builder.py b/tests/test_builder.py
index 3d19d8e..2ef9c80 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -152,7 +152,7 @@ class TestCollectHelpers:
         params = _collect_extra_params("out.png", config)
         assert params["width"] == 512
         assert params["height"] == 256
-        assert params["reference_images"] == ("ref.png",)
+        assert params["reference_images"] == ["ref.png"]
 
     def test_collect_extra_params_empty(self, write_config: WriteConfig) -> None:
         config = write_config({"targets": {"out.txt": {"prompt": "x"}}})