diff --git a/litellm/utils.py b/litellm/utils.py
index 2830a9e0abf..97d621b4e6e 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -2701,9 +2701,10 @@ def register_model(model_cost: Union[str, dict]):
                 if builtin_entry is None:
                     base_model = value.get("base_model")
                     if isinstance(base_model, str) and base_model:
-                        builtin_entry = _resolve_builtin_model_cost_entry(
-                            key=base_model, provider=provider
-                        ) or litellm.model_cost.get(base_model)
+                        builtin_entry = _resolve_builtin_model_cost_entry(key=base_model, provider=provider)
+                        if builtin_entry is None:
+                            base_model_cost = litellm.model_cost.get(base_model)
+                            builtin_entry = dict(base_model_cost) if base_model_cost is not None else None
                 if builtin_entry is not None:
                     for field in _CACHE_PRICING_FIELDS:
                         if value.get(field) is None and builtin_entry.get(field) is not None: