diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala
index 8f7f10243d4c..0f831c155e4a 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/aggregate/HashAggregateExec.scala
@@ -174,8 +174,8 @@ case class HashAggregateExec(
     }
   }
 
-  // The variables used as aggregation buffer. Only used for aggregation without keys.
-  private var bufVars: Seq[ExprCode] = _
+  // The variables used as aggregation buffer. Only used in codegen for aggregation without keys.
+  @transient private var bufVars: Seq[ExprCode] = _
 
   private def doProduceWithoutKeys(ctx: CodegenContext): String = {
     val initAgg = ctx.addMutableState(CodeGenerator.JAVA_BOOLEAN, "initAgg")
@@ -236,6 +236,8 @@ case class HashAggregateExec(
          | }
        """.stripMargin)
 
+    bufVars = null  // explicitly null this field out to allow the referent to be GC'd sooner
+
     val numOutput = metricTerm(ctx, "numOutputRows")
     val aggTime = metricTerm(ctx, "aggTime")
     val beforeAgg = ctx.freshName("beforeAgg")