diff --git a/src/anthropic/_models.py b/src/anthropic/_models.py
index dc00516b..98ea7239 100644
--- a/src/anthropic/_models.py
+++ b/src/anthropic/_models.py
@@ -668,7 +668,7 @@ def construct_type(*, value: object, type_: object, metadata: Optional[List[Any]
         if not is_list(value):
             return value
 
-        inner_type = args[0]  # List[inner_type]
+        inner_type = args[0] if args else object  # List[inner_type] or bare list
         return [construct_type(value=entry, type_=inner_type) for entry in value]
 
     if origin == float:
diff --git a/tests/test_models.py b/tests/test_models.py
index 195f2307..94cb47a2 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -1014,4 +1014,9 @@ class Model(BaseModel):
 
     # falls back to list of chars rather than calling str(["h", "e", "l", "l", "o"])
     assert m.data["items"] == ["h", "e", "l", "l", "o"]
-    assert m.model_dump()["data"]["items"] == ["h", "e", "l", "l", "o"]
+
+
+def test_construct_type_bare_list() -> None:
+    # Bare list (no type parameter) must not raise IndexError
+    result = construct_type(value=["a", "b", "c"], type_=list)
+    assert result == ["a", "b", "c"]