diff --git a/tests/config/test_model_arch_config.py b/tests/config/test_model_arch_config.py
index e172983b54f4..46790be6e4e1 100644
--- a/tests/config/test_model_arch_config.py
+++ b/tests/config/test_model_arch_config.py
@@ -6,6 +6,7 @@
 from pathlib import Path
 
 import pytest
+from transformers import PretrainedConfig
 
 from vllm.config import ModelConfig, ParallelConfig, SpeculativeConfig
 from vllm.transformers_utils.model_arch_config_convertor import (
@@ -114,6 +115,22 @@ def _assert_model_config_methods(
         assert model_config.get_head_size() == expected["head_size"]
 
 
+def test_head_size_falls_back_when_head_dim_is_zero():
+    """Regression test for configs that materialize missing head_dim as 0."""
+    hf_config = PretrainedConfig(
+        model_type="deepseek_vl_v2",
+        hidden_size=1280,
+        num_attention_heads=10,
+        num_key_value_heads=10,
+        head_dim=0,
+        kv_lora_rank=None,
+    )
+
+    convertor = ModelArchConfigConvertorBase(hf_config, hf_config)
+
+    assert convertor.get_head_size() == 128
+
+
 @pytest.mark.parametrize("model", BASE_MODELS_TO_TEST)
 def test_base_model_arch_config(model: str):
     """Test model architecture config for base models."""
diff --git a/vllm/transformers_utils/model_arch_config_convertor.py b/vllm/transformers_utils/model_arch_config_convertor.py
index 250aee503786..fa0fe7d5d66b 100644
--- a/vllm/transformers_utils/model_arch_config_convertor.py
+++ b/vllm/transformers_utils/model_arch_config_convertor.py
@@ -58,9 +58,12 @@ def get_head_size(self) -> int:
                 if qk_rope_head_dim and qk_nope_head_dim:
                     return qk_rope_head_dim + qk_nope_head_dim
 
-        # NOTE: Some configs may set head_dim=None in the config
-        if getattr(self.hf_text_config, "head_dim", None) is not None:
-            return self.hf_text_config.head_dim
+        # NOTE: Some config classes may set head_dim=None or materialize a missing
+        # head_dim as 0 (for example, DeepseekVLV2TextConfig).
+        if (
+            head_dim := getattr(self.hf_text_config, "head_dim", None)
+        ) is not None and head_dim > 0:
+            return head_dim
 
         # NOTE: Some models (such as PLaMo2.1) use `hidden_size_per_head`
         if getattr(self.hf_text_config, "hidden_size_per_head", None) is not None: