diff --git a/src/main/scala/Testing.scala b/src/main/scala/Testing.scala
index a010975b..a194915e 100644
--- a/src/main/scala/Testing.scala
+++ b/src/main/scala/Testing.scala
@@ -165,7 +165,7 @@ object TestGenerator extends App with FileSystemUtilities {
   val v = createOutputFile(configClassName + ".knb")
   v.write(world.getKnobs)
   v.close
-  val d = new java.io.FileOutputStream(Driver.targetDir + configClassName + ".dtb")
+  val d = new java.io.FileOutputStream(Driver.targetDir + "/" + configClassName + ".dtb")
   d.write(paramsFromConfig(DeviceTree))
   d.close
   val w = createOutputFile(configClassName + ".cst")