diff --git a/vllm/model_executor/layers/kda.py b/vllm/model_executor/layers/kda.py
index 308bc8be1dece..26458f2e3c4da 100644
--- a/vllm/model_executor/layers/kda.py
+++ b/vllm/model_executor/layers/kda.py
@@ -259,7 +259,7 @@ class KimiDeltaAttention(nn.Module, MambaBase):
         hidden_states: torch.Tensor,
         positions: torch.Tensor,
         output: torch.Tensor,
-    ) -> torch.Tensor:
+    ) -> None:
         num_tokens = hidden_states.size(0)
         q = self.q_proj(hidden_states)[0]
         k = self.k_proj(hidden_states)[0]
@@ -291,8 +291,7 @@ class KimiDeltaAttention(nn.Module, MambaBase):
         )
         core_attn_out = self.o_norm(core_attn_out, g2)
         core_attn_out = rearrange(core_attn_out, "1 n h d -> n (h d)")
-
-        return self.o_proj(core_attn_out)[0]
+        output[:] = self.o_proj(core_attn_out)[0]
 
     def _forward(
         self,