diff --git a/vllm/model_executor/models/qwen3_5.py b/vllm/model_executor/models/qwen3_5.py
index 61ff6946c..808db2d6f 100644
--- a/vllm/model_executor/models/qwen3_5.py
+++ b/vllm/model_executor/models/qwen3_5.py
@@ -870,8 +870,9 @@ class Qwen3_5ForConditionalGeneration(Qwen3VLForConditionalGeneration, IsHybrid)
         cls,
         vllm_config: "VllmConfig",
     ) -> tuple[torch.dtype, torch.dtype]:
+        mamba_ssm_dtype = vllm_config.model_config.hf_text_config.mamba_ssm_dtype
         return MambaStateDtypeCalculator.gated_delta_net_state_dtype(
-            vllm_config.model_config.dtype, vllm_config.cache_config.mamba_cache_dtype
+            vllm_config.model_config.dtype, mamba_ssm_dtype
         )
 
     @classmethod