diff --git a/src/anthropic/_models.py b/src/anthropic/_models.py
index dc00516b..ac1b212b 100644
--- a/src/anthropic/_models.py
+++ b/src/anthropic/_models.py
@@ -647,7 +647,8 @@ def construct_type(*, value: object, type_: object, metadata: Optional[List[Any]
         if not is_mapping(value):
             return value
 
-        _, items_type = get_args(type_)  # Dict[_, items_type]
+        args = get_args(type_)
+        items_type = args[1] if len(args) >= 2 else object  # Dict[_, items_type]
         return {key: construct_type(value=item, type_=items_type) for key, item in value.items()}
 
     if (
@@ -668,7 +669,7 @@ 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]
         return [construct_type(value=entry, type_=inner_type) for entry in value]
 
     if origin == float:
diff --git a/src/anthropic/_utils/_transform.py b/src/anthropic/_utils/_transform.py
index 1331da17..0229f3d5 100644
--- a/src/anthropic/_utils/_transform.py
+++ b/src/anthropic/_utils/_transform.py
@@ -180,7 +180,8 @@ def _transform_recursive(
         return _transform_typeddict(data, stripped_type)
 
     if origin == dict and is_mapping(data):
-        items_type = get_args(stripped_type)[1]
+        args = get_args(stripped_type)
+        items_type = args[1] if len(args) >= 2 else object
         return {key: _transform_recursive(value, annotation=items_type) for key, value in data.items()}
 
     if (
@@ -348,7 +349,8 @@ async def _async_transform_recursive(
         return await _async_transform_typeddict(data, stripped_type)
 
     if origin == dict and is_mapping(data):
-        items_type = get_args(stripped_type)[1]
+        args = get_args(stripped_type)
+        items_type = args[1] if len(args) >= 2 else object
         return {key: _transform_recursive(value, annotation=items_type) for key, value in data.items()}
 
     if (
diff --git a/tests/test_models.py b/tests/test_models.py
index 195f2307..d7e5850f 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -655,6 +655,18 @@ class Model(BaseModel):
     assert m.value == "foo"
 
 
+def test_bare_dict_annotation() -> None:
+    # a bare `dict` annotation (no type parameters) should not raise
+    m = construct_type(value={"key": "value", "n": 1}, type_=cast(Any, dict))
+    assert m == {"key": "value", "n": 1}
+
+
+def test_bare_list_annotation() -> None:
+    # a bare `list` annotation (no type parameters) should not raise
+    m = construct_type(value=["a", "b", 1], type_=cast(Any, list))
+    assert m == ["a", "b", 1]
+
+
 def test_discriminated_unions_invalid_data() -> None:
     class A(BaseModel):
         type: Literal["a"]
diff --git a/tests/test_transform.py b/tests/test_transform.py
index 513b09ca..406d838d 100644
--- a/tests/test_transform.py
+++ b/tests/test_transform.py
@@ -61,6 +61,13 @@ class Baz2(TypedDict):
     my_baz: Annotated[str, PropertyInfo(alias="myBaz")]
 
 
+@parametrize
+@pytest.mark.asyncio
+async def test_bare_dict_annotation(use_async: bool) -> None:
+    # a bare `dict` annotation (no type parameters) should pass values through unchanged
+    assert await transform({"key": "value", "n": 1}, cast(Any, dict), use_async) == {"key": "value", "n": 1}
+
+
 @parametrize
 @pytest.mark.asyncio
 async def test_recursive_typeddict(use_async: bool) -> None: