diff --git a/llama_stack/apis/scoring_functions/scoring_functions.py b/llama_stack/apis/scoring_functions/scoring_functions.py
index 6b90aea6d..2e5bf0aef 100644
--- a/llama_stack/apis/scoring_functions/scoring_functions.py
+++ b/llama_stack/apis/scoring_functions/scoring_functions.py
@@ -44,7 +44,9 @@ class ScoringFnDef(BaseModel):
         description="List of parameters for the deterministic function",
         default_factory=list,
     )
-    return_type: ParamType
+    return_type: ParamType = Field(
+        description="The return type of the deterministic function",
+    )
     context: Optional[LLMAsJudgeContext] = None
     # We can optionally add information here to support packaging of code, etc.