Encountering type error when following tutorial

[mttsweet]

Hello, I'm following the tutorial: https://python.langchain.com/docs/tutorials/chatbot/#prompt-templates

Everything works up until I add a prompt template after which the invoke method of the prompt template throws this error:

Argument of type "MessagesState" cannot be assigned to parameter "input" of type "dict[Unknown, Unknown]" in function "invoke"
  "MessagesState" is not assignable to "dict[Unknown, Unknown]" [reportArgumentType]

I imagine this is a problem with my code and not the library, but I'm having trouble tracking down the issue. My full code looks like this:

from langchain_core.messages import HumanMessage
from langchain_core.prompts import ChatPromptTemplate, MessagesPlaceholder
from langchain_ollama import ChatOllama
from langgraph.checkpoint.memory import MemorySaver
from langgraph.graph import START, MessagesState, StateGraph

llm = ChatOllama(model="gemma3:1b", temperature=0)

workflow = StateGraph(state_schema=MessagesState)


def call_model(state: MessagesState):
    prompt = prompt_template.invoke(state)
    response = llm.invoke(prompt)
    return {"messages": response}


workflow.add_edge(START, "model")
workflow.add_node("model", call_model)

prompt_template = ChatPromptTemplate.from_messages(
    [
        (
            "system",
            "You talk like a pirate.",
        ),
        MessagesPlaceholder(variable_name="messages"),
    ]
)

memory = MemorySaver()
app = workflow.compile(checkpointer=memory)

config = {"configurable": {"thread_id": "32485"}}

while True:
    user_input = input("=> ")
    if user_input.lower() in ["quit", "exit", "q", "bye"]:
        print("Goodbye!")
        break
    input_messages = [HumanMessage(user_input)]
    output = app.invoke({"messages": input_messages}, config)
    output["messages"][-1].pretty_print()