diff --git a/src/fmu/sumo/explorer/objects/surface_collection.py b/src/fmu/sumo/explorer/objects/surface_collection.py
index f22bedb2..d73849d1 100644
--- a/src/fmu/sumo/explorer/objects/surface_collection.py
+++ b/src/fmu/sumo/explorer/objects/surface_collection.py
@@ -136,7 +136,7 @@ def _aggregate(self, operation: str) -> RegularSurface:
             res = self._sumo.post(
                 "/aggregations",
                 json={
-                    "operation": [operation],
+                    "operations": [operation],
                     "object_ids": object_ids,
                     "class": "surface",
                 },