diff --git a/vllm/platforms/cpu.py b/vllm/platforms/cpu.py
index 4e0683b8a2de1..179ee6a7d2478 100644
--- a/vllm/platforms/cpu.py
+++ b/vllm/platforms/cpu.py
@@ -35,7 +35,7 @@ class CpuPlatform(Platform):
                              dtype: torch.dtype, kv_cache_dtype: Optional[str],
                              block_size: int, use_v1: bool,
                              use_mla: bool) -> str:
-        if selected_backend != _Backend.TORCH_SDPA:
+        if selected_backend and selected_backend != _Backend.TORCH_SDPA:
             logger.info("Cannot use %s backend on CPU.", selected_backend)
         logger.info("Using Torch SDPA backend.")
         return "vllm.attention.backends.torch_sdpa.TorchSDPABackend"