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 52d0450afb181..100048f603ad0 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
@@ -159,7 +159,11 @@ case class HashAggregateExec(
 
   // The variables are used as aggregation buffers and each aggregate function has one or more
   // ExprCode to initialize its buffer slots. Only used for aggregation without keys.
-  private var bufVars: Seq[Seq[ExprCode]] = _
+  private val bufVar = new ThreadLocal[Seq[Seq[ExprCode]]] {
+    override def initialValue(): Seq[Seq[ExprCode]] = {
+      Seq.empty
+    }
+  }
 
   private def doProduceWithoutKeys(ctx: CodegenContext): String = {
     val initAgg = ctx.addMutableState(CodeGenerator.JAVA_BOOLEAN, "initAgg")
@@ -169,7 +173,7 @@ case class HashAggregateExec(
     // generate variables for aggregation buffer
     val functions = aggregateExpressions.map(_.aggregateFunction.asInstanceOf[DeclarativeAggregate])
     val initExpr = functions.map(f => f.initialValues)
-    bufVars = initExpr.map { exprs =>
+    val localBufVars = initExpr.map { exprs =>
       exprs.map { e =>
         val isNull = ctx.addMutableState(CodeGenerator.JAVA_BOOLEAN, "bufIsNull")
         val value = ctx.addMutableState(CodeGenerator.javaType(e.dataType), "bufValue")
@@ -185,7 +189,8 @@ case class HashAggregateExec(
           JavaCode.global(value, e.dataType))
       }
     }
-    val flatBufVars = bufVars.flatten
+    bufVars.set(localBufVars)
+    val flatBufVars = bufVars.get().flatten
     val initBufVar = evaluateVariables(flatBufVars)
 
     // generate variables for output
@@ -322,7 +327,7 @@ case class HashAggregateExec(
           e.aggregateFunction.asInstanceOf[DeclarativeAggregate].mergeExpressions
       }
     }
-    ctx.currentVars = bufVars.flatten ++ input
+    ctx.currentVars = bufVars.get().flatten ++ input
     val boundUpdateExprs = updateExprs.map { updateExprsForOneFunc =>
       bindReferences(updateExprsForOneFunc, inputAttrs)
     }
@@ -336,7 +341,7 @@ case class HashAggregateExec(
 
     val aggNames = functions.map(_.prettyName)
     val aggCodeBlocks = bufferEvals.zipWithIndex.map { case (bufferEvalsForOneFunc, i) =>
-      val bufVarsForOneFunc = bufVars(i)
+      val bufVarsForOneFunc = bufVars.get()(i)
       // All the update code for aggregation buffers should be placed in the end
       // of each aggregation function code.
       val updates = bufferEvalsForOneFunc.zip(bufVarsForOneFunc).map { case (ev, bufVar) =>