diff --git a/vllm/models/qwen4_exp/amd/qsa.py b/vllm/models/qwen4_exp/amd/qsa.py
index 325e0e3d91..3f03b293b4 100644
--- a/vllm/models/qwen4_exp/amd/qsa.py
+++ b/vllm/models/qwen4_exp/amd/qsa.py
@@ -214,7 +214,7 @@ class Qwen4ExpQSAAttention(Qwen3NextAttention, AttentionLayerBase):
         elif tp_size % self.total_num_kv_heads:
             raise ValueError("TP size must be divisible by replicated QSA KV heads")
         self.num_kv_heads = max(1, self.total_num_kv_heads // tp_size)
-        self.head_dim = int(config.head_dim or self.hidden_size // self.num_heads)
+        self.head_dim = int(config.head_dim or self.hidden_size // self.total_num_heads)
         self.q_size = self.num_heads * self.head_dim
         self.kv_size = self.num_kv_heads * self.head_dim
         self.scaling = self.head_dim**-0.5
diff --git a/vllm/models/qwen4_exp/nvidia/qsa.py b/vllm/models/qwen4_exp/nvidia/qsa.py
index a20fcdeec9..0246db8094 100644
--- a/vllm/models/qwen4_exp/nvidia/qsa.py
+++ b/vllm/models/qwen4_exp/nvidia/qsa.py
@@ -393,7 +393,7 @@ class Qwen4ExpQSAAttention(Qwen3NextAttention, AttentionLayerBase):
         elif tp_size % self.total_num_kv_heads:
             raise ValueError("TP size must be divisible by replicated QSA KV heads")
         self.num_kv_heads = max(1, self.total_num_kv_heads // tp_size)
-        self.head_dim = int(config.head_dim or self.hidden_size // self.num_heads)
+        self.head_dim = int(config.head_dim or self.hidden_size // self.total_num_heads)
         self.q_size = self.num_heads * self.head_dim
         self.kv_size = self.num_kv_heads * self.head_dim
         self.scaling = self.head_dim**-0.5