diff --git a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/SourceSet.kt b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/SourceSet.kt
index c094b82c..1ca707ca 100644
--- a/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/SourceSet.kt
+++ b/modules/kobalt-plugin-api/src/main/kotlin/com/beust/kobalt/internal/SourceSet.kt
@@ -8,15 +8,17 @@ enum class SourceSet {
     MAIN,
     TEST;
 
+    private fun unknown(sourceSet: SourceSet) = throw KobaltException("Unknown source set: $this")
+
     fun correctSourceSet(project: Project) =
         if (this == SourceSet.MAIN) project.sourceDirectories
         else if (this == SourceSet.TEST) project.sourceDirectoriesTest
-        else throw KobaltException("Unknown source set: $this")
+        else unknown(this)
 
     fun correctOutputDir(project: Project) =
         if (this == SourceSet.MAIN) KFiles.CLASSES_DIR
         else if (this == SourceSet.TEST) KFiles.TEST_CLASSES_DIR
-        else throw IllegalArgumentException("Unknown source set: $this")
+        else unknown(this)
 
     companion object {
         fun of(isTest: Boolean) = if (isTest) TEST else MAIN