diff --git a/src/backend/distributed/executor/multi_client_executor.c b/src/backend/distributed/executor/multi_client_executor.c
index f5f0df1cc..da852d5c1 100644
--- a/src/backend/distributed/executor/multi_client_executor.c
+++ b/src/backend/distributed/executor/multi_client_executor.c
@@ -883,7 +883,7 @@ MultiClientWait(WaitInfo *waitInfo)
 		}
 		else if (rc == 0)
 		{
-			ereport(DEBUG2,
+			ereport(DEBUG5,
 					(errmsg("waiting for activity on tasks took longer than %ld ms",
 							(long) RemoteTaskCheckInterval * 10)));
 		}
diff --git a/src/backend/distributed/executor/multi_task_tracker_executor.c b/src/backend/distributed/executor/multi_task_tracker_executor.c
index e08657e98..8bdcdacd3 100644
--- a/src/backend/distributed/executor/multi_task_tracker_executor.c
+++ b/src/backend/distributed/executor/multi_task_tracker_executor.c
@@ -519,6 +519,15 @@ TaskHashCreate(uint32 taskHashSize)
 	int hashFlags = 0;
 	HTAB *taskHash = NULL;
 
+	/*
+	 * Can't create a hashtable of size 0. Normally that shouldn't happen, but
+	 * shard pruning currently can lead to this (Job with 0 Tasks). See #833.
+	 */
+	if (taskHashSize == 0)
+	{
+		taskHashSize = 2;
+	}
+
 	memset(&info, 0, sizeof(info));
 	info.keysize = sizeof(TaskMapKey);
 	info.entrysize = sizeof(TaskMapEntry);
diff --git a/src/backend/distributed/planner/multi_master_planner.c b/src/backend/distributed/planner/multi_master_planner.c
index 05a522e6e..5efd68fc5 100644
--- a/src/backend/distributed/planner/multi_master_planner.c
+++ b/src/backend/distributed/planner/multi_master_planner.c
@@ -134,6 +134,7 @@ BuildAggregatePlan(Query *masterQuery, Plan *subPlan)
 	Assert(masterQuery->hasAggs || masterQuery->groupClause);
 
 	aggregateTargetList = masterQuery->targetList;
+	memset(&aggregateCosts, 0, sizeof(AggClauseCosts));
 	count_agg_clauses(NULL, (Node *) aggregateTargetList, &aggregateCosts);
 
 	/*