diff --git a/src/adapter/cli-to-openai.ts b/src/adapter/cli-to-openai.ts
index 1e43eab..bb5f638 100644
--- a/src/adapter/cli-to-openai.ts
+++ b/src/adapter/cli-to-openai.ts
@@ -102,7 +102,8 @@ export function cliResultToOpenai(
  * Normalize Claude model names to a consistent format
  * e.g., "claude-sonnet-4-5-20250929" -> "claude-sonnet-4"
  */
-function normalizeModelName(model: string): string {
+function normalizeModelName(model: string | undefined): string {
+  if (!model) return "claude-sonnet-4";
   if (model.includes("opus")) return "claude-opus-4";
   if (model.includes("sonnet")) return "claude-sonnet-4";
   if (model.includes("haiku")) return "claude-haiku-4";