diff --git a/vllm/model_executor/model_loader/loader.py b/vllm/model_executor/model_loader/loader.py
index 5bcae37961195..140b61fe6d56a 100644
--- a/vllm/model_executor/model_loader/loader.py
+++ b/vllm/model_executor/model_loader/loader.py
@@ -94,18 +94,34 @@ def _initialize_model(vllm_config: VllmConfig, prefix: str = "") -> nn.Module:
     model_config = vllm_config.model_config
     model_class, _ = get_model_architecture(model_config)
     signatures = inspect.signature(model_class.__init__)
-    # collect all kw-only parameters
-    kw_only_params = [
-        param.name for param in signatures.parameters.values()
-        if param.kind == inspect.Parameter.KEYWORD_ONLY
-    ]
-    assert "vllm_config" in kw_only_params and "prefix" in kw_only_params, \
-    ("vLLM model class must accept `vllm_config` and `prefix` as kw-only "
-    "arguments. Possibly you have an old-style model class registered from "
-    "out of tree and it is used for new vLLM version. "
-    "Please check https://docs.vllm.ai/en/latest/design/class_hierarchy.html "
-    "for the design and update the model class accordingly.")
-    return model_class(vllm_config=vllm_config, prefix=prefix)
+    all_params = [param.name for param in signatures.parameters.values()]
+    if "vllm_config" in all_params and "prefix" in all_params:
+        # new-style model class
+        return model_class(vllm_config=vllm_config, prefix=prefix)
+    msg = ("vLLM model class should accept `vllm_config` and `prefix` as "
+           "input arguments. Possibly you have an old-style model class"
+           " registered from out of tree and it is used for new vLLM version. "
+           "Check https://docs.vllm.ai/en/latest/design/class_hierarchy.html "
+           "for the design and update the model class accordingly.")
+    logger.warning(msg)
+    logger.warning(
+        "Trying to guess the arguments for old-style model class %s",
+        model_class)
+    # try to be compatible with old-style model class
+    kwargs = {}
+    if "prefix" in all_params:
+        kwargs["prefix"] = prefix
+    if "config" in all_params:
+        kwargs["config"] = model_config.hf_config
+    if "cache_config" in all_params:
+        kwargs["cache_config"] = vllm_config.cache_config
+    if "quant_config" in all_params:
+        kwargs["quant_config"] = vllm_config.quant_config
+    if "lora_config" in all_params:
+        kwargs["lora_config"] = vllm_config.lora_config
+    if "scheduler_config" in all_params:
+        kwargs["scheduler_config"] = vllm_config.scheduler_config
+    return model_class(**kwargs)
 
 
 class BaseModelLoader(ABC):