diff --git a/langchain/chat_models/anthropic.py b/langchain/chat_models/anthropic.py
index 023c9e41..edb03652 100644
--- a/langchain/chat_models/anthropic.py
+++ b/langchain/chat_models/anthropic.py
@@ -76,6 +76,8 @@ class ChatAnthropic(BaseChatModel, _AnthropicCommon):
         Returns:
             str: Combined string with necessary HUMAN_PROMPT and AI_PROMPT tags.
         """
+        messages = messages.copy()  # don't mutate the original list
+
         if not self.AI_PROMPT:
             raise NameError("Please ensure the anthropic package is loaded")
 
diff --git a/tests/integration_tests/chat_models/test_anthropic.py b/tests/integration_tests/chat_models/test_anthropic.py
index a7186c8b..f0c2de79 100644
--- a/tests/integration_tests/chat_models/test_anthropic.py
+++ b/tests/integration_tests/chat_models/test_anthropic.py
@@ -24,6 +24,22 @@ def test_anthropic_call() -> None:
     assert isinstance(response.content, str)
 
 
+def test_anthropic_generate() -> None:
+    """Test generate method of anthropic."""
+    chat = ChatAnthropic(model="test")
+    chat_messages: List[List[BaseMessage]] = [
+        [HumanMessage(content="How many toes do dogs have?")]
+    ]
+    messages_copy = [messages.copy() for messages in chat_messages]
+    result: LLMResult = chat.generate(chat_messages)
+    assert isinstance(result, LLMResult)
+    for response in result.generations[0]:
+        assert isinstance(response, ChatGeneration)
+        assert isinstance(response.text, str)
+        assert response.text == response.message.content
+    assert chat_messages == messages_copy
+
+
 def test_anthropic_streaming() -> None:
     """Test streaming tokens from anthropic."""
     chat = ChatAnthropic(model="test", streaming=True)