diff --git a/buildscripts/cost_model/join_calibration_settings.py b/buildscripts/cost_model/join_calibration_settings.py
index af2d0421587..3cf0bab42b6 100644
--- a/buildscripts/cost_model/join_calibration_settings.py
+++ b/buildscripts/cost_model/join_calibration_settings.py
@@ -108,7 +108,10 @@ def create_join_collection_template(
                 indexed=False,
             ),
         ],
-        compound_indexes=[],
+        # Need an index for multikeyness info
+        compound_indexes=[
+            ["dummy", "unique", "random", "uniform_16", "uniform_256", "uniform_4k", "uniform_64k"]
+        ],
         cardinalities=[COLLECTION_CARDINALITY],
     )
 
diff --git a/buildscripts/cost_model/join_start.py b/buildscripts/cost_model/join_start.py
index 08e589d2d62..21912f194f9 100644
--- a/buildscripts/cost_model/join_start.py
+++ b/buildscripts/cost_model/join_start.py
@@ -488,6 +488,8 @@ async def main():
             "internalMeasureQueryExecutionTimeInNanoseconds=true",
             "--setParameter",
             "internalEnableJoinOptimization=true",
+            "--setParameter",
+            "featureFlagPathArrayness=true",
         ],
     ) as manager:
         generator = DataGenerator(manager.database, join_data_generator)