diff --git a/libs/core/tests/unit_tests/test_prompt_values.py b/libs/core/tests/unit_tests/test_prompt_values.py
new file mode 100644
index 00000000000..625cd51202b
--- /dev/null
+++ b/libs/core/tests/unit_tests/test_prompt_values.py
@@ -0,0 +1,28 @@
+import pytest
+
+from langchain_core.messages import (
+    AIMessage,
+    AIMessageChunk,
+    HumanMessage,
+    HumanMessageChunk,
+    SystemMessage,
+    SystemMessageChunk,
+    ToolMessage,
+    ToolMessageChunk,
+)
+from langchain_core.prompt_values import ChatPromptValueConcrete
+
+
+@pytest.mark.xfail(reason="Broken union type.")
+def test_chat_prompt_value_concrete() -> None:
+    messages: list = [
+        AIMessage("foo"),
+        HumanMessage("foo"),
+        SystemMessage("foo"),
+        ToolMessage("foo", tool_call_id="foo"),
+        AIMessageChunk(content="foo"),
+        HumanMessageChunk(content="foo"),
+        SystemMessageChunk(content="foo"),
+        ToolMessageChunk(content="foo", tool_call_id="foo"),
+    ]
+    assert ChatPromptValueConcrete(messages=messages).messages == messages