diff --git a/biopet-tools/src/main/scala/nl/lumc/sasc/biopet/tools/bamstats/Stats.scala b/biopet-tools/src/main/scala/nl/lumc/sasc/biopet/tools/bamstats/Stats.scala
index 07b1459269d90a807559e1fe3ff448b6146ca3b0..aa3a58963412ef376681c3a43560d5339ceca65f 100644
--- a/biopet-tools/src/main/scala/nl/lumc/sasc/biopet/tools/bamstats/Stats.scala
+++ b/biopet-tools/src/main/scala/nl/lumc/sasc/biopet/tools/bamstats/Stats.scala
@@ -19,7 +19,7 @@ case class Stats() {
   val _5_ClippingHistogram = Histogram()
   val _3_ClippingHistogram = Histogram()
 
-  def +(other: Stats): Stats = {
+  def +=(other: Stats): Stats = {
     this.totalReads += other.totalReads
     this.unmapped += other.unmapped
     this.mappingQualityHistogram += other.mappingQualityHistogram