diff --git a/src/core/chorus/OpenAICompletionsAPIUtils.ts b/src/core/chorus/OpenAICompletionsAPIUtils.ts
index ec057da1..300a5e1b 100644
--- a/src/core/chorus/OpenAICompletionsAPIUtils.ts
+++ b/src/core/chorus/OpenAICompletionsAPIUtils.ts
@@ -199,7 +199,7 @@ function convertToolCalls(
     // adapted from a snippet on https://platform.openai.com/docs/guides/function-calling?api-mode=chat&lang=javascript
     // which appears to be severely buggy (lol)
     for (const chunk of chunks) {
-        const toolCallDeltas = chunk.choices[0].delta.tool_calls || [];
+        const toolCallDeltas = chunk.choices?.[0]?.delta?.tool_calls || [];
         for (const toolCallDelta of toolCallDeltas) {
             const index = toolCallDelta.index ?? 0;