diff --git a/legacy/src/chatgpt-api.ts b/legacy/src/chatgpt-api.ts
index 17792d66..c2367454 100644
--- a/legacy/src/chatgpt-api.ts
+++ b/legacy/src/chatgpt-api.ts
@@ -349,13 +349,13 @@ export class ChatGPTAPI {
         .reduce((prompt, message) => {
           switch (message.role) {
             case 'system':
-              return [prompt, `Instructions:\n${message.content}`]
+              return [...prompt, `Instructions:\n${message.content}`]
             case 'user':
-              return [prompt, `${userLabel}:\n${message.content}`]
+              return [...prompt, `${userLabel}:\n${message.content}`]
             default:
-              return [prompt, `${assistantLabel}:\n${message.content}`]
+              return [...prompt, `${assistantLabel}:\n${message.content}`]
           }
-        }, [])
+        }, [] as string[])
         .join('\n\n')
 
       const nextNumTokensEstimate = await this._getTokenCount(prompt)