diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate2/aggregates.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate2/aggregates.scala
index b14fac2ae9a37..11f35e69ae46f 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate2/aggregates.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/aggregate2/aggregates.scala
@@ -110,7 +110,7 @@ abstract class AggregateFunction2
   def bufferSchema: StructType
 
   /** Attributes of fields in bufferSchema. */
-  def bufferAttributes: Seq[Attribute]
+  def bufferAttributes: Seq[AttributeReference]
 
   /** Clones bufferAttributes. */
   def cloneBufferAttributes: Seq[Attribute]
@@ -147,7 +147,7 @@ case class MyDoubleSum(child: Expression) extends AggregateFunction2 {
   override val bufferSchema: StructType =
     StructType(StructField("currentSum", DoubleType, true) :: Nil)
 
-  override val bufferAttributes: Seq[Attribute] = bufferSchema.toAttributes
+  override val bufferAttributes: Seq[AttributeReference] = bufferSchema.toAttributes
 
   override lazy val cloneBufferAttributes = bufferAttributes.map(_.newInstance())
 
@@ -205,8 +205,8 @@ abstract class AlgebraicAggregate extends AggregateFunction2 with Serializable {
   override lazy val cloneBufferAttributes = bufferAttributes.map(_.newInstance())
 
   implicit class RichAttribute(a: AttributeReference) {
-    def left = a
-    def right = cloneBufferAttributes(bufferAttributes.indexOf(a))
+    def left: AttributeReference = a
+    def right: AttributeReference = cloneBufferAttributes(bufferAttributes.indexOf(a))
   }
 
   /** An AlgebraicAggregate's bufferSchema is derived from bufferAttributes. */
@@ -277,4 +277,4 @@ case class Average(child: Expression) extends AlgebraicAggregate {
   override def nullable: Boolean = true
   override def dataType: DataType = resultType
   override def children: Seq[Expression] = child :: Nil
-}
\ No newline at end of file
+}
diff --git a/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala b/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
index 75bbef5b5f9ed..446679240911d 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala
@@ -21,8 +21,6 @@ import java.beans.Introspector
 import java.util.Properties
 import java.util.concurrent.atomic.AtomicReference
 
-import org.apache.spark.sql.execution.aggregate2.{CheckAggregateFunction, ConvertAggregateFunction}
-
 import scala.collection.JavaConversions._
 import scala.collection.immutable
 import scala.language.implicitConversions
@@ -42,6 +40,7 @@ import org.apache.spark.sql.catalyst.plans.logical.{LocalRelation, LogicalPlan}
 import org.apache.spark.sql.catalyst.rules.RuleExecutor
 import org.apache.spark.sql.catalyst.{InternalRow, ParserDialect, _}
 import org.apache.spark.sql.execution.{Filter, _}
+import org.apache.spark.sql.execution.aggregate2.{CheckAggregateFunction, ConvertAggregateFunction}
 import org.apache.spark.sql.sources._
 import org.apache.spark.sql.types._
 import org.apache.spark.unsafe.types.UTF8String
diff --git a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
index 138fa0515115a..4e7d2e0062761 100644
--- a/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
+++ b/sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveContext.scala
@@ -21,8 +21,6 @@ import java.io.File
 import java.net.{URL, URLClassLoader}
 import java.sql.Timestamp
 
-import org.apache.spark.sql.execution.aggregate2.{CheckAggregateFunction, ConvertAggregateFunction}
-
 import scala.collection.JavaConversions._
 import scala.collection.mutable.HashMap
 import scala.language.implicitConversions
@@ -46,6 +44,7 @@ import org.apache.spark.sql.catalyst.ParserDialect
 import org.apache.spark.sql.catalyst.analysis._
 import org.apache.spark.sql.catalyst.plans.logical._
 import org.apache.spark.sql.execution.{ExecutedCommand, ExtractPythonUDFs, SetCommand}
+import org.apache.spark.sql.execution.aggregate2.{CheckAggregateFunction, ConvertAggregateFunction}
 import org.apache.spark.sql.hive.client._
 import org.apache.spark.sql.hive.execution.{DescribeHiveTableCommand, HiveNativeCommand}
 import org.apache.spark.sql.sources.DataSourceStrategy