diff --git a/mkdocs/config/config_options.py b/mkdocs/config/config_options.py
index 9f160e82..ee75b047 100644
--- a/mkdocs/config/config_options.py
+++ b/mkdocs/config/config_options.py
@@ -95,7 +95,7 @@ class SubConfig(Generic[SomeConfig], BaseConfigOption[SomeConfig]):
 
         if self._do_validation:
             # Capture errors and warnings
-            self.warnings = [f"Sub-option '{key}': {msg}" for key, msg in warnings]
+            self.warnings.extend(f"Sub-option '{key}': {msg}" for key, msg in warnings)
             if failed:
                 # Get the first failing one
                 key, err = failed[0]
@@ -188,6 +188,7 @@ class ListOfItems(Generic[T], BaseConfigOption[List[T]]):
         fake_keys = [f'{parent_key_name}[{i}]' for i in range(len(value))]
         fake_config.data = dict(zip(fake_keys, value))
 
+        self.option_type.warnings = self.warnings
         for key_name in fake_config:
             self.option_type.pre_validation(fake_config, key_name)
         for key_name in fake_config:
diff --git a/mkdocs/tests/config/config_options_tests.py b/mkdocs/tests/config/config_options_tests.py
index 952f4ce9..f82a1de9 100644
--- a/mkdocs/tests/config/config_options_tests.py
+++ b/mkdocs/tests/config/config_options_tests.py
@@ -678,6 +678,19 @@ class ListOfItemsTest(TestCase):
         with self.expect_error(option="'asdf' is not a valid port"):
             self.get_config(Schema, {'option': ["localhost:8000", "1.2.3.4:asdf"]})
 
+    def test_warning(self) -> None:
+        class Schema(Config):
+            option = c.ListOfItems(c.Deprecated())
+
+        self.get_config(
+            Schema,
+            {'option': ['a']},
+            warnings=dict(
+                option="The configuration option 'option[0]' has been "
+                "deprecated and will be removed in a future release."
+            ),
+        )
+
 
 class FilesystemObjectTest(TestCase):
     def test_valid_dir(self) -> None: