diff --git a/chatmastermind/ais/openai.py b/chatmastermind/ais/openai.py
index a8ceb34..e3ce5a6 100644
--- a/chatmastermind/ais/openai.py
+++ b/chatmastermind/ais/openai.py
@@ -150,7 +150,7 @@ class OpenAI(AI):
         for message in chat.messages:
             if message.answer:
                 prompt_tokens += append('user', message.question)
-                prompt_tokens += append('assistant', message.answer)
+                prompt_tokens += append('assistant', str(message.answer))
         if question:
             prompt_tokens += append('user', question.question)
         return oai_chat, prompt_tokens