diff --git a/vllm/model_executor/models/deepseek_v4.py b/vllm/model_executor/models/deepseek_v4.py
index 0b762d50fe72..01aa922f3c29 100644
--- a/vllm/model_executor/models/deepseek_v4.py
+++ b/vllm/model_executor/models/deepseek_v4.py
@@ -715,12 +715,15 @@ def __init__(
         config = vllm_config.model_config.hf_config
         quant_config = vllm_config.quant_config
         self.prefix = prefix
-        if vllm_config.parallel_config.enable_expert_parallel:
-            self.use_mega_moe = (
-                vllm_config.kernel_config.moe_backend == "deep_gemm_mega_moe"
+        self.use_mega_moe = (
+            vllm_config.kernel_config.moe_backend == "deep_gemm_mega_moe"
+        )
+        if self.use_mega_moe and not vllm_config.parallel_config.enable_expert_parallel:
+            raise NotImplementedError(
+                "DeepSeek V4 MegaMoE currently requires expert parallel. "
+                "Enable it with --enable-expert-parallel, or pick a different "
+                "moe backend."
             )
-        else:
-            self.use_mega_moe = False
 
         self.routed_scaling_factor = getattr(config, "routed_scaling_factor", 1.0)
         self.hidden_size = config.hidden_size
@@ -1223,12 +1226,15 @@ def __init__(self, *, vllm_config: VllmConfig, prefix: str = ""):
         config = vllm_config.model_config.hf_config
         quant_config = vllm_config.quant_config
         self.config = config
-        if vllm_config.parallel_config.enable_expert_parallel:
-            self.use_mega_moe = (
-                vllm_config.kernel_config.moe_backend == "deep_gemm_mega_moe"
+        self.use_mega_moe = (
+            vllm_config.kernel_config.moe_backend == "deep_gemm_mega_moe"
+        )
+        if self.use_mega_moe and not vllm_config.parallel_config.enable_expert_parallel:
+            raise NotImplementedError(
+                "DeepSeek V4 MegaMoE currently requires expert parallel. "
+                "Enable it with --enable-expert-parallel, or pick a different "
+                "moe backend."
             )
-        else:
-            self.use_mega_moe = False
         self.vocab_size = config.vocab_size
         self.hc_eps = config.hc_eps
         self.hc_mult = config.hc_mult