diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index 3bc78331e4..9c5d6e66a2 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -3570,6 +3570,11 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
 				{
 					int			length = phasedata->gset_lengths[i];
 
+					/* nothing to do for empty grouping set */
+					if (length == 0)
+						continue;
+
+					/* if we already had one of this length, it'll do */
 					if (phasedata->eqfunctions[length - 1] != NULL)
 						continue;