diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index 6b274751ba..f2bb5502b2 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -2454,7 +2454,11 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
 		aggstate->hash_pergroup = pergroups;
 
 		find_hash_columns(aggstate);
-		build_hash_table(aggstate);
+
+		/* Skip massive memory allocation if we are just doing EXPLAIN */
+		if (!(eflags & EXEC_FLAG_EXPLAIN_ONLY))
+			build_hash_table(aggstate);
+
 		aggstate->table_filled = false;
 	}