diff --git a/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala b/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
index b284b636f2766465cc9f8eaab9eff7f812cffb99..5366c1a1cc1bd54e6d2615883d02e490b9cf0068 100644
--- a/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
+++ b/core/src/main/scala/org/apache/spark/rdd/CoGroupedRDD.scala
@@ -185,6 +185,7 @@ class CoGroupedRDD[K](@transient var rdds: Seq[RDD[_ <: Product2[K, _]]], part:
           combiner1(depNum) ++= combiner2(depNum)
           depNum += 1
         }
+        combiner1
       }
     new ExternalAppendOnlyMap[K, CoGroupValue, CoGroupCombiner](
       createCombiner, mergeValue, mergeCombiners)