diff --git a/vllm/model_executor/layers/deepseek_compressor.py b/vllm/model_executor/layers/deepseek_compressor.py
index 48628fec46e0..41dc85682b05 100644
--- a/vllm/model_executor/layers/deepseek_compressor.py
+++ b/vllm/model_executor/layers/deepseek_compressor.py
@@ -13,6 +13,7 @@
 from vllm.model_executor.layers.layernorm import RMSNorm
 from vllm.model_executor.layers.linear import (
     MergedColumnParallelLinear,
+    UnquantizedLinearMethod,
 )
 from vllm.platforms import current_platform
 from vllm.triton_utils import tl, triton
@@ -226,6 +227,11 @@ def __init__(
             prefix=f"{prefix}.fused_wkv_wgate",
         )
         self.norm = RMSNorm(self.head_dim, self.rms_norm_eps)
+        if not isinstance(self.fused_wkv_wgate.quant_method, UnquantizedLinearMethod):
+            raise NotImplementedError(
+                "Quantization of `indexer.compressor.wkv/wgate` is not supported "
+                "due to accuracy concerns. See #42001."
+            )
 
         self.state_cache = CompressorStateCache(
             state_dim=2 * self.coff * self.head_dim,  # kv_state + score_state
diff --git a/vllm/model_executor/layers/deepseek_v4_attention.py b/vllm/model_executor/layers/deepseek_v4_attention.py
index 494d61338084..087ef375aa5b 100644
--- a/vllm/model_executor/layers/deepseek_v4_attention.py
+++ b/vllm/model_executor/layers/deepseek_v4_attention.py
@@ -16,6 +16,7 @@
 import vllm.envs as envs
 from vllm.model_executor.layers.linear import (
     ReplicatedLinear,
+    UnquantizedLinearMethod,
 )
 from vllm.model_executor.layers.sparse_attn_indexer import SparseAttnIndexer
 from vllm.utils.deep_gemm import fp8_einsum
@@ -284,6 +285,17 @@ def __init__(
                 k_cache_prefix=self.mla_attn.prefix,
             )
 
+        # For now, model requires fp8 quantization for attention
+        # assume that there exists a `wo` weight scale
+        if hasattr(self.wo_a, "weight_scale_inv"):
+            self.wo_scale_name = "weight_scale_inv"
+        elif hasattr(self.wo_a, "weight_scale"):
+            self.wo_scale_name = "weight_scale"
+        else:
+            raise NotImplementedError(
+                "DeepSeekV4 requires FP8 quantization of `attn.wo_a.weight`"
+            )
+
     def forward(
         self,
         positions: torch.Tensor,
@@ -334,7 +346,7 @@ def forward(
         )
 
         wo_a_fp8 = self.wo_a.weight
-        wo_a_scale = self.wo_a.weight_scale_inv
+        wo_a_scale = getattr(self.wo_a, self.wo_scale_name)
 
         z = torch.empty(
             (num_tokens, self.n_local_groups, self.o_lora_rank),
@@ -1133,6 +1145,8 @@ def __init__(
         )
         self.k_norm = LayerNorm(self.head_dim, eps=1e-6)
         self.softmax_scale = self.head_dim**-0.5
+        if not isinstance(self.weights_proj.quant_method, UnquantizedLinearMethod):
+            raise NotImplementedError("Quantization of `attn.indexer.weights_proj`")
 
         self.scale_fmt = "ue8m0"
         self.quant_block_size = 128  # TODO: get from config
diff --git a/vllm/model_executor/models/deepseek_v4.py b/vllm/model_executor/models/deepseek_v4.py
index cef4038dc2e6..34bb083bb4f3 100644
--- a/vllm/model_executor/models/deepseek_v4.py
+++ b/vllm/model_executor/models/deepseek_v4.py
@@ -143,6 +143,9 @@ def __init__(self, *args, **kwargs):
         # ``is_scale_e8m0`` is a property that resolves on first read,
         # by which time the current vllm_config has been set.
 
+        # implicitly ignored layers for DSV4
+        self.ignored_layers += ["weights_proj", "fused_wkv_wgate"]
+
     @property
     def expert_dtype(self) -> str:
         if self._resolved_expert_dtype is None:
@@ -1004,7 +1007,14 @@ def __init__(
             prefix=f"{prefix}.wo_b",
         )
         self.softmax_scale = self.head_dim**-0.5
-        self.scale_fmt = config.quantization_config["scale_fmt"]
+        # scale_fmt is only used in the indexer (for C4A layers), not in
+        # the main attention. Default to "ue8m0" for compatibility.
+        self.scale_fmt = (
+            config.quantization_config.get("scale_fmt", "ue8m0")
+            if hasattr(config, "quantization_config")
+            and isinstance(config.quantization_config, dict)
+            else "ue8m0"
+        )
 
         self.rope_parameters = config.rope_scaling
 
@@ -1442,7 +1452,7 @@ def get_expert_mapping(self) -> list[tuple[str, str, int, str]]:
         first_layer = next(iter(islice(self.layers, self.start_layer, self.end_layer)))
         if first_layer.ffn.use_mega_moe:
             return make_deepseek_v4_expert_params_mapping(self.config.n_routed_experts)
-        # Params for weights, fp8 weight scales, fp8 activation scales
+        # Params for unfused moe weights
         # (param_name, weight_name, expert_id, shard_id)
         return FusedMoE.make_expert_params_mapping(
             self,