diff --git a/public/gears/src/main/scala/nl/lumc/sasc/biopet/pipelines/gears/CombineReads.scala b/public/gears/src/main/scala/nl/lumc/sasc/biopet/pipelines/gears/CombineReads.scala
index 608afa3c0945e05e5c669ba8737393ea13109da3..f8cddedfd99753443787f858e294258cea292665 100644
--- a/public/gears/src/main/scala/nl/lumc/sasc/biopet/pipelines/gears/CombineReads.scala
+++ b/public/gears/src/main/scala/nl/lumc/sasc/biopet/pipelines/gears/CombineReads.scala
@@ -28,15 +28,15 @@ class CombineReads(val root: Configurable) extends QScript with SummaryQScript w
   private lazy val forwardPrimers: List[String] = config("forward_primers", default = Nil)
   private lazy val reversePrimers: List[String] = config("reverse_primers", default = Nil)
 
-  def combinedFastq: File = if ((forwardPrimers :: reversePrimers).nonEmpty)
+  def combinedFastq: File = if ((forwardPrimers ::: reversePrimers).nonEmpty)
     swapExt(outputDir, flash.combinedFastq, ".fastq.gz", ".clip.fastq.gz")
   else flash.combinedFastq
 
-  def notCombinedR1Fastq: File = if ((forwardPrimers :: reversePrimers).nonEmpty)
+  def notCombinedR1Fastq: File = if ((forwardPrimers ::: reversePrimers).nonEmpty)
     swapExt(outputDir, flash.notCombinedR1, ".fastq.gz", ".clip.fastq.gz")
   else flash.notCombinedR1
 
-  def notCombinedR2Fastq: File = if ((forwardPrimers :: reversePrimers).nonEmpty)
+  def notCombinedR2Fastq: File = if ((forwardPrimers ::: reversePrimers).nonEmpty)
     swapExt(outputDir, flash.notCombinedR2, ".fastq.gz", ".clip.fastq.gz")
   else flash.notCombinedR2