diff --git a/vllm/config/model.py b/vllm/config/model.py
index 96dbf9725..749af0d5d 100644
--- a/vllm/config/model.py
+++ b/vllm/config/model.py
@@ -1119,6 +1119,9 @@ class ModelConfig:
     @cached_property
     def is_mm_prefix_lm(self) -> bool:
         """Whether to use bidirectional attention for mm positions."""
+        if hasattr(self.hf_config, "is_mm_prefix_lm"):
+            return bool(self.hf_config.is_mm_prefix_lm)
+        # fallback to list of known models
         MM_PREFIX_LM_MODELS = (
             "gemma3",
             "molmo2",