diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index fe5c47e533..65cfcb1eb9 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -1399,7 +1399,7 @@ project_aggregates(AggState *aggstate)
 }
 
 /*
- * Walk tlist and qual to find referenced colnos, dividing them into
+ * Find input-tuple columns that are needed, dividing them into
  * aggregated and unaggregated sets.
  */
 static void
@@ -1412,9 +1412,15 @@ find_cols(AggState *aggstate, Bitmapset **aggregated, Bitmapset **unaggregated)
 	context.aggregated = NULL;
 	context.unaggregated = NULL;
 
+	/* Examine tlist and quals */
 	(void) find_cols_walker((Node *) agg->plan.targetlist, &context);
 	(void) find_cols_walker((Node *) agg->plan.qual, &context);
 
+	/* In some cases, grouping columns will not appear in the tlist */
+	for (int i = 0; i < agg->numCols; i++)
+		context.unaggregated = bms_add_member(context.unaggregated,
+											  agg->grpColIdx[i]);
+
 	*aggregated = context.aggregated;
 	*unaggregated = context.unaggregated;
 }