diff --git a/libs/vertexai/langchain_google_vertexai/_anthropic_utils.py b/libs/vertexai/langchain_google_vertexai/_anthropic_utils.py
index 6ca2f12c..f36dfa18 100644
--- a/libs/vertexai/langchain_google_vertexai/_anthropic_utils.py
+++ b/libs/vertexai/langchain_google_vertexai/_anthropic_utils.py
@@ -3,7 +3,12 @@
 
 from langchain_core.messages import BaseMessage
 
-_message_type_lookups = {"human": "user", "ai": "assistant"}
+_message_type_lookups = {
+    "human": "user",
+    "ai": "assistant",
+    "AIMessageChunk": "assistant",
+    "HumanMessageChunk": "user",
+}
 
 
 def _format_image(image_url: str) -> Dict: