diff --git a/chatmastermind/ais/openai.py b/chatmastermind/ais/openai.py
index 0e7ad41..d7bb12f 100644
--- a/chatmastermind/ais/openai.py
+++ b/chatmastermind/ais/openai.py
@@ -44,7 +44,7 @@ class OpenAI(AI):
             frequency_penalty=self.config.frequency_penalty,
             presence_penalty=self.config.presence_penalty)
         question.answer = Answer(response['choices'][0]['message']['content'])
-        question.tags = otags
+        question.tags = set(otags) if otags is not None else None
         question.ai = self.ID
         question.model = self.config.model
         answers: list[Message] = [question]