mongos> db.test.aggregate([{"$match":{"c32":17}}, {"$group":{"_id":null, "total":{"$sum":"$float"}}}])
2019-12-30T19:59:16.398+0800 E QUERY    [js] Error: command failed: {
    "ok" : 0,
    "errmsg" : "unrecognized field 'mergeByPBRT'",
    "code" : 9,
    "codeName" : "FailedToParse",
    "operationTime" : Timestamp(1577707153, 1),
    "$clusterTime" : {
        "clusterTime" : Timestamp(1577707155, 3),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    }
}

diff --git a/src/mongo/s/commands/cluster_aggregate.cpp b/src/mongo/s/commands/cluster_aggregate.cpp
index d58ce76220..a2c308a353 100644
--- a/src/mongo/s/commands/cluster_aggregate.cpp
+++ b/src/mongo/s/commands/cluster_aggregate.cpp
@@ -215,7 +215,9 @@ BSONObj createCommandForTargetedShards(
             targetedCmd[AggregationRequest::kNeedsMergeName] = Value(true);
             // If this is a change stream, set the 'mergeByPBRT' flag on the command. This notifies
             // the shards that the mongoS is capable of merging streams based on resume token.
-            targetedCmd[AggregationRequest::kMergeByPBRTName] = Value(litePipe.hasChangeStream());
+            if (litePipe.hasChangeStream()) {
+                targetedCmd[AggregationRequest::kMergeByPBRTName] = Value(litePipe.hasChangeStream());
+            }
             targetedCmd[AggregationRequest::kCursorName] =
                 Value(DOC(AggregationRequest::kBatchSizeName << 0));
         }