diff --git a/pydantic_settings/sources.py b/pydantic_settings/sources.py
index 30e7fa33..7400b8f0 100644
--- a/pydantic_settings/sources.py
+++ b/pydantic_settings/sources.py
@@ -2115,13 +2115,16 @@ def read_env_file(
 def _annotation_is_complex(annotation: type[Any] | None, metadata: list[Any]) -> bool:
     # If the model is a root model, the root annotation should be used to
     # evaluate the complexity.
-    if annotation is not None and inspect.isclass(annotation) and issubclass(annotation, RootModel):
-        # In some rare cases (see test_root_model_as_field),
-        # the root attribute is not available. For these cases, python 3.8 and 3.9
-        # return 'RootModelRootType'.
-        root_annotation = annotation.__annotations__.get('root', None)
-        if root_annotation is not None and root_annotation != 'RootModelRootType':
-            annotation = root_annotation
+    try:
+        if annotation is not None and issubclass(annotation, RootModel):
+            # In some rare cases (see test_root_model_as_field),
+            # the root attribute is not available. For these cases, python 3.8 and 3.9
+            # return 'RootModelRootType'.
+            root_annotation = annotation.__annotations__.get('root', None)
+            if root_annotation is not None and root_annotation != 'RootModelRootType':
+                annotation = root_annotation
+    except TypeError:
+        pass
 
     if any(isinstance(md, Json) for md in metadata):  # type: ignore[misc]
         return False
diff --git a/tests/test_settings.py b/tests/test_settings.py
index d91695b3..62f073c6 100644
--- a/tests/test_settings.py
+++ b/tests/test_settings.py
@@ -4994,3 +4994,13 @@ class Settings(BaseSettings):
     s = Settings()
     assert s.POSTGRES_USER == 'postgres'
     assert s.model_dump() == {'POSTGRES_USER': 'postgres', 'postgres_name': 'name', 'postgres_user_2': 'postgres2'}
+
+
+@pytest.mark.skipif(sys.version_info < (3, 9), reason='requires python 3.9 or higher')
+def test_annotation_is_complex_root_model_check():
+    """Test for https://github.com/pydantic/pydantic-settings/issues/390"""
+
+    class Settings(BaseSettings):
+        foo: list[str] = []
+
+    Settings()