diff --git a/workflows_api/runtime/src/schema_helpers.py b/workflows_api/runtime/src/schema_helpers.py
index 35544ff4..f1d4a351 100644
--- a/workflows_api/runtime/src/schema_helpers.py
+++ b/workflows_api/runtime/src/schema_helpers.py
@@ -43,7 +43,7 @@ class TemporalExtent(BaseModel):
     startdate: datetime
     enddate: datetime
 
-    @root_validator
+    @root_validator(pre=True)
     def check_dates(cls, v):
         if v["startdate"] >= v["enddate"]:
             raise ValueError("Invalid extent - startdate must be before enddate")