diff --git a/shiny/ui/_chat_normalize.py b/shiny/ui/_chat_normalize.py
index 85da7ed9c..2c8612878 100644
--- a/shiny/ui/_chat_normalize.py
+++ b/shiny/ui/_chat_normalize.py
@@ -57,11 +57,15 @@ def can_normalize_chunk(self, chunk: Any) -> bool:
 
 class DictNormalizer(BaseMessageNormalizer):
     def normalize(self, message: Any) -> ChatMessage:
-        x = self._check_dict(message)
+        x = cast("dict[str, Any]", message)
+        if "content" not in x:
+            raise ValueError("Message must have 'content' key")
         return ChatMessage(content=x["content"], role=x.get("role", "assistant"))
 
     def normalize_chunk(self, chunk: Any) -> ChatMessage:
-        x = self._check_dict(chunk)
+        x = cast("dict[str, Any]", chunk)
+        if "content" not in x:
+            raise ValueError("Message must have 'content' key")
         return ChatMessage(content=x["content"], role=x.get("role", "assistant"))
 
     def can_normalize(self, message: Any) -> bool:
@@ -70,14 +74,6 @@ def can_normalize(self, message: Any) -> bool:
     def can_normalize_chunk(self, chunk: Any) -> bool:
         return isinstance(chunk, dict)
 
-    @staticmethod
-    def _check_dict(x: Any) -> "dict[str, Any]":
-        if "content" not in x:
-            raise ValueError("Message must have 'content' key")
-        if "role" in x and x["role"] not in ["assistant", "system"]:
-            raise ValueError("Role must be 'assistant' or 'system")
-        return x
-
 
 class LangChainNormalizer(BaseMessageNormalizer):
     def normalize(self, message: Any) -> ChatMessage:
diff --git a/tests/playwright/shiny/components/chat/append_user_msg/app.py b/tests/playwright/shiny/components/chat/append_user_msg/app.py
new file mode 100644
index 000000000..835ce7204
--- /dev/null
+++ b/tests/playwright/shiny/components/chat/append_user_msg/app.py
@@ -0,0 +1,18 @@
+from shiny import reactive
+from shiny.express import render, ui
+
+chat = ui.Chat(id="chat")
+chat.ui()
+
+
+@reactive.effect
+async def _():
+    await chat.append_message({"content": "A user message", "role": "user"})
+
+
+"chat.messages():"
+
+
+@render.code
+def message_state():
+    return str(chat.messages())
diff --git a/tests/playwright/shiny/components/chat/append_user_msg/test_chat_append_user_msg.py b/tests/playwright/shiny/components/chat/append_user_msg/test_chat_append_user_msg.py
new file mode 100644
index 000000000..1d4e614e6
--- /dev/null
+++ b/tests/playwright/shiny/components/chat/append_user_msg/test_chat_append_user_msg.py
@@ -0,0 +1,19 @@
+from playwright.sync_api import Page, expect
+
+from shiny.playwright import controller
+from shiny.run import ShinyAppProc
+
+
+def test_validate_chat_append_user_message(page: Page, local_app: ShinyAppProc) -> None:
+    page.goto(local_app.url)
+
+    chat = controller.Chat(page, "chat")
+
+    # Verify starting state
+    expect(chat.loc).to_be_visible()
+    chat.expect_latest_message("A user message")
+
+    # Verify that the message state is as expected
+    message_state = controller.OutputCode(page, "message_state")
+    message_state_expected = ({"content": "A user message", "role": "user"},)
+    message_state.expect_value(str(message_state_expected))