diff --git a/compile/persist/src/main/scala/sbt/inc/TextAnalysisFormat.scala b/compile/persist/src/main/scala/sbt/inc/TextAnalysisFormat.scala
index 59e432493..a23a87725 100644
--- a/compile/persist/src/main/scala/sbt/inc/TextAnalysisFormat.scala
+++ b/compile/persist/src/main/scala/sbt/inc/TextAnalysisFormat.scala
@@ -357,7 +357,7 @@ object TextAnalysisFormat {
 						val outputDirectory = outputAsMap(singleOutputKey)
 					}
 					case `multipleOutputMode` => new MultipleOutput {
-						val outputGroups = outputAsMap.toArray.map {
+						val outputGroups: Array[MultipleOutput.OutputGroup] = outputAsMap.toArray.map {
 							case (src: File, out: File) => new MultipleOutput.OutputGroup {
 								val sourceDirectory = src
 								val outputDirectory = out