diff --git a/qwen_asr/core/vllm_backend/qwen3_asr.py b/qwen_asr/core/vllm_backend/qwen3_asr.py
index db36219..49fb183 100644
--- a/qwen_asr/core/vllm_backend/qwen3_asr.py
+++ b/qwen_asr/core/vllm_backend/qwen3_asr.py
@@ -977,8 +977,9 @@ def get_generation_prompt(
                 f"Unsupported task_type '{task_type}'. "
                 "Supported task types are 'transcribe' and 'translate'."
             )
-        full_lang_name_to = cls.supported_languages.get(to_language, to_language)
-        if to_language is None:
+        effective_language = to_language or language
+        full_lang_name_to = cls.supported_languages.get(effective_language, effective_language)
+        if effective_language is None:
             prompt = (
                 f"<|im_start|>user\n{audio_placeholder}<|im_end|>\n"
                 f"<|im_start|>assistant\n"