diff --git a/api/services/dataset_service.py b/api/services/dataset_service.py
index ea8896a5aa..1332390d46 100644
--- a/api/services/dataset_service.py
+++ b/api/services/dataset_service.py
@@ -170,6 +170,16 @@ class _AutomaticProcessRule(BaseModel):
     mode: Literal[ProcessRuleMode.AUTOMATIC]
     summary_index_setting: _SummaryIndexSetting | None = None
 
+    @field_validator("summary_index_setting", mode="before")
+    @classmethod
+    def _normalize_summary_index_setting(cls, v: Any) -> Any:
+        """Treat dicts with enable=None (or missing enable) as None (#36602)."""
+        if v is None:
+            return None
+        if isinstance(v, dict) and v.get("enable") is None:
+            return None
+        return v
+
 
 class _CustomProcessRule(BaseModel):
     model_config = ConfigDict(extra="allow")
@@ -178,6 +188,16 @@ class _CustomProcessRule(BaseModel):
     rules: _EstimateRules
     summary_index_setting: _SummaryIndexSetting | None = None
 
+    @field_validator("summary_index_setting", mode="before")
+    @classmethod
+    def _normalize_summary_index_setting(cls, v: Any) -> Any:
+        """Treat dicts with enable=None (or missing enable) as None (#36602)."""
+        if v is None:
+            return None
+        if isinstance(v, dict) and v.get("enable") is None:
+            return None
+        return v
+
 
 class _HierarchicalProcessRule(BaseModel):
     model_config = ConfigDict(extra="allow")
@@ -186,6 +206,16 @@ class _HierarchicalProcessRule(BaseModel):
     rules: _EstimateRules
     summary_index_setting: _SummaryIndexSetting | None = None
 
+    @field_validator("summary_index_setting", mode="before")
+    @classmethod
+    def _normalize_summary_index_setting(cls, v: Any) -> Any:
+        """Treat dicts with enable=None (or missing enable) as None (#36602)."""
+        if v is None:
+            return None
+        if isinstance(v, dict) and v.get("enable") is None:
+            return None
+        return v
+
 
 _EstimateProcessRule = Annotated[
     _AutomaticProcessRule | _CustomProcessRule | _HierarchicalProcessRule,